Rules Reference¶

This page is an index of available rules which are bundled with SQLFluff.

For information on how to configure which rules are enabled for your project see Enabling and Disabling Rules.
If you just want to turn rules on or off for specific files, or specific sections of files, see Ignoring Errors & Files.
For more information on how to configure the rules which you do enable see Rule Configuration.

Core Rules¶

Certain rules belong to the core rule group. In order for a rule to be designated as core, it must meet the following criteria:

Stable
Applies to most dialects
Could detect a syntax issue
Isn’t too opinionated toward one style (e.g. the dbt style guide)

Core rules can also make it easier to roll out SQLFluff to a team by only needing to follow a ‘common sense’ subset of rules initially, rather than spending time understanding and configuring all the rules, some of which your team may not necessarily agree with.

We believe teams will eventually want to enforce more than just the core rules, and we encourage everyone to explore all the rules and customize a rule set that best suites their organization.

See the Configuration section for more information on how to enable only core rules by default.

Rule Index¶

Bundle	Rule Name	Code	Aliases
Aliasing bundle	`aliasing.table`	`AL01`	L011
	`aliasing.column`	`AL02`	L012
	`aliasing.expression`	`AL03`	L013
	`aliasing.unique.table`	`AL04`	L020
	`aliasing.unused`	`AL05`	L025
	`aliasing.length`	`AL06`	L066
	`aliasing.forbid`	`AL07`	L031
	`aliasing.unique.column`	`AL08`
	`aliasing.self_alias.column`	`AL09`
Ambiguous bundle	`ambiguous.distinct`	`AM01`	L021
	`ambiguous.union`	`AM02`	L033
	`ambiguous.order_by`	`AM03`	L037
	`ambiguous.column_count`	`AM04`	L044
	`ambiguous.join`	`AM05`	L051
	`ambiguous.column_references`	`AM06`	L054
	`ambiguous.set_columns`	`AM07`	L068
	`ambiguous.join_condition`	`AM08`
Capitalisation bundle	`capitalisation.keywords`	`CP01`	L010
	`capitalisation.identifiers`	`CP02`	L014
	`capitalisation.functions`	`CP03`	L030
	`capitalisation.literals`	`CP04`	L040
	`capitalisation.types`	`CP05`	L063
Convention bundle	`convention.not_equal`	`CV01`	L061
	`convention.coalesce`	`CV02`	L060
	`convention.select_trailing_comma`	`CV03`	L038
	`convention.count_rows`	`CV04`	L047
	`convention.is_null`	`CV05`	L049
	`convention.terminator`	`CV06`	L052
	`convention.statement_brackets`	`CV07`	L053
	`convention.left_join`	`CV08`	L055
	`convention.blocked_words`	`CV09`	L062
	`convention.quoted_literals`	`CV10`	L064
	`convention.casting_style`	`CV11`	L067
	`convention.join_condition`	`CV12`
Jinja bundle	`jinja.padding`	`JJ01`	L046
Layout bundle	`layout.spacing`	`LT01`	L001, L005, L006, L008, L023, L024, L039, L048, L071
	`layout.indent`	`LT02`	L002, L003, L004
	`layout.operators`	`LT03`	L007
	`layout.commas`	`LT04`	L019
	`layout.long_lines`	`LT05`	L016
	`layout.functions`	`LT06`	L017
	`layout.cte_bracket`	`LT07`	L018
	`layout.cte_newline`	`LT08`	L022
	`layout.select_targets`	`LT09`	L036
	`layout.select_modifiers`	`LT10`	L041
	`layout.set_operators`	`LT11`	L065
	`layout.end_of_file`	`LT12`	L009, layout.end-of-file
	`layout.start_of_file`	`LT13`	L050
	`layout.keyword_newline`	`LT14`
References bundle	`references.from`	`RF01`	L026
	`references.qualification`	`RF02`	L027
	`references.consistent`	`RF03`	L028
	`references.keywords`	`RF04`	L029
	`references.special_chars`	`RF05`	L057
	`references.quoting`	`RF06`	L059
Structure bundle	`structure.else_null`	`ST01`	L035
	`structure.simple_case`	`ST02`	L043
	`structure.unused_cte`	`ST03`	L045
	`structure.nested_case`	`ST04`	L058
	`structure.subquery`	`ST05`	L042
	`structure.column_order`	`ST06`	L034
	`structure.using`	`ST07`	L032
	`structure.distinct`	`ST08`	L015
	`structure.join_condition_order`	`ST09`
	`structure.constant_expression`	`ST10`
	`structure.unused_join`	`ST11`
TSQL bundle	`tsql.sp_prefix`	`TQ01`	L056

Aliasing bundle¶

Code AL01¶

Rule aliasing.table¶

Implicit/explicit aliasing of table.¶

Aliasing of table to follow preference (requiring an explicit AS is the default).

This rule is sqlfluff fix compatible.

Name: aliasing.table

Aliases: L011

Groups: all, aliasing

Configuration

aliasing: Should alias have an explicit AS or is implicit aliasing required? Must be one of ['implicit', 'explicit'].

Anti-pattern

In this example, the alias voo is implicit.

SELECT
    voo.a
FROM foo voo

Best practice

Add AS to make it explicit.

SELECT
    voo.a
FROM foo AS voo

Code AL02¶

Rule aliasing.column¶

Implicit/explicit aliasing of columns.¶

Aliasing of columns to follow preference (explicit using an AS clause is default).

Name: aliasing.column

Aliases: L012

Groups: all, core, aliasing

Configuration

aliasing: Should alias have an explicit AS or is implicit aliasing required? Must be one of ['implicit', 'explicit'].

Anti-pattern

In this example, the alias for column a is implicit.

SELECT
    a alias_col
FROM foo

Best practice

Add AS to make it explicit.

SELECT
    a AS alias_col
FROM foo

Code AL03¶

Rule aliasing.expression¶

Column expression without alias. Use explicit AS clause.¶

Name: aliasing.expression

Aliases: L013

Groups: all, core, aliasing

Configuration

allow_scalar: Whether or not to allow a single element in the select clause to be without an alias. Must be one of [True, False].

Anti-pattern

In this example, there is no alias for both sums.

SELECT
    sum(a),
    sum(b)
FROM foo

Best practice

Add aliases.

SELECT
    sum(a) AS a_sum,
    sum(b) AS b_sum
FROM foo

Code AL04¶

Rule aliasing.unique.table¶

Table aliases should be unique within each clause.¶

Reusing table aliases is very likely a coding error.

Name: aliasing.unique.table

Aliases: L020

Groups: all, core, aliasing, aliasing.unique

Anti-pattern

In this example, the alias t is reused for two different tables:

SELECT
    t.a,
    t.b
FROM foo AS t, bar AS t

-- This can also happen when using schemas where the
-- implicit alias is the table name:

SELECT
    a,
    b
FROM
    2020.foo,
    2021.foo

Best practice

Make all tables have a unique alias.

SELECT
    f.a,
    b.b
FROM foo AS f, bar AS b

-- Also use explicit aliases when referencing two tables
-- with the same name from two different schemas.

SELECT
    f1.a,
    f2.b
FROM
    2020.foo AS f1,
    2021.foo AS f2

Code AL05¶

Rule aliasing.unused¶

Tables should not be aliased if that alias is not used.¶

This rule is sqlfluff fix compatible.

Name: aliasing.unused

Aliases: L025

Groups: all, core, aliasing

Configuration

alias_case_check: How to handle comparison casefolding in an alias. Must be one of ['dialect', 'case_insensitive', 'quoted_cs_naked_upper', 'quoted_cs_naked_lower', 'case_sensitive'].

Anti-pattern

SELECT
    a
FROM foo AS zoo

Best practice

Use the alias or remove it. An unused alias makes code harder to read without changing any functionality.

SELECT
    zoo.a
FROM foo AS zoo

-- Alternatively...

SELECT
    a
FROM foo

Code AL06¶

Rule aliasing.length¶

Enforce table alias lengths in from clauses and join conditions.¶

Name: aliasing.length

Aliases: L066

Groups: all, core, aliasing

Configuration

max_alias_length: The maximum length of an alias to allow without raising a violation. Must be one of range(0, 1000).
min_alias_length: The minimum length of an alias to allow without raising a violation. Must be one of range(0, 1000).

Anti-pattern

In this example, alias o is used for the orders table.

SELECT
    SUM(o.amount) as order_amount,
FROM orders as o

Best practice

Avoid aliases. Avoid short aliases when aliases are necessary.

Avoid table aliases in from clauses and join conditions.¶

This rule is sqlfluff fix compatible.

Name: aliasing.forbid

Aliases: L031

Groups: all, aliasing

Configuration

force_enable: Run this rule even for dialects where this rule is disabled by default. Must be one of [True, False].

Note

This rule was taken from the dbt Style Guide which notes that:

Avoid table aliases in join conditions (especially initialisms) - it’s harder to understand what the table called “c” is compared to “customers”.

This rule is controversial and for many larger databases avoiding alias is neither realistic nor desirable. In particular for BigQuery due to the complexity of backtick requirements and determining whether a name refers to a project or dataset so automated fixes can potentially break working SQL code. For most users AL06 is likely a more appropriate linting rule to drive a sensible behaviour around aliasing.

The stricter treatment of aliases in this rule may be useful for more focused projects, or temporarily as a refactoring tool because the fix routine of the rule can remove aliases.

This rule is disabled by default for all dialects it can be enabled with the force_enable = True flag.

Anti-pattern

In this example, alias o is used for the orders table, and c is used for customers table.

SELECT
    COUNT(o.customer_id) as order_amount,
    c.name
FROM orders as o
JOIN customers as c on o.id = c.user_id

Best practice

Avoid aliases.

SELECT
    COUNT(orders.customer_id) as order_amount,
    customers.name
FROM orders
JOIN customers on orders.id = customers.user_id

-- Self-join will not raise issue

SELECT
    table1.a,
    table_alias.b,
FROM
    table1
    LEFT JOIN table1 AS table_alias ON
        table1.foreign_key = table_alias.foreign_key

Code AL08¶

Rule aliasing.unique.column¶

Column aliases should be unique within each clause.¶

Reusing column aliases is very likely a coding error. Note that while in many dialects, quoting an identifier makes it case-sensitive this rule always compares in a case-insensitive way. This is because columns with the same name, but different case, are still confusing and potentially ambiguous to other readers.

In situations where it is necessary to have columns with the same name (whether they differ in case or not) we recommend disabling this rule for either just the line, or the whole file.

Name: aliasing.unique.column

Groups: all, core, aliasing, aliasing.unique

Anti-pattern

In this example, the alias foo is reused for two different columns:

SELECT
    a as foo,
    b as foo
FROM tbl;

-- This can also happen when referencing the same column
-- column twice, or aliasing an expression to the same
-- name as a column:

SELECT
    foo,
    foo,
    a as foo
FROM tbl;

Best practice

Make all columns have a unique alias.

SELECT
    a as foo,
    b as bar
FROM tbl;

-- Avoid also using the same column twice unless aliased:

SELECT
    foo as foo1,
    foo as foo2,
    a as foo3
FROM tbl;

Code AL09¶

Rule aliasing.self_alias.column¶

Column aliases should not alias to itself, i.e. self-alias.¶

Renaming the column to itself is a redundant piece of SQL, which doesn’t affect its functionality. This rule only applies when aliasing to an exact copy of the column reference (e.g. foo as foo or "BAR" as "BAR", see note below on more complex examples). Aliases which effectively change the casing of an identifier are still allowed.

This rule is sqlfluff fix compatible.

Name: aliasing.self_alias.column

Groups: all, core, aliasing

Note

This rule works in conjunction with references.quoting (RF06) and capitalisation.identifiers (CP02) to handle self aliases with mixed quoting and casing. In the situation that these two rules are not enabled then this rule will only fix the strict case where the quoting and casing of the alias and reference are the same.

If those two rules are enabled, the fixes applied may result in a situation where this rule can kick in as a secondary effect. For example this Snowflake query:

-- Original Query. AL09 will not trigger because casing and
-- quoting are different. RF06 will however fix the unnecessary
-- quoting of "COL".
SELECT "COL" AS col FROM table;
-- After RF06, the query will look like this, at which point
-- CP02 will see the inconsistent capitalisation. Depending
-- on the configuration it will change one of the identifiers.
-- Let's assume the default configuration of "consistent".
SELECT COL AS col FROM table;
-- After CP02, the alias and the reference will be the same
-- and at this point AL09 can take over and remove the alias.
SELECT COL AS COL FROM table;
-- ..resulting in:
SELECT COL FROM table;

This interdependence between the rules, and the configuration options offered by each one means a variety of outcomes can be achieved by enabling and disabling each one. See Enabling and Disabling Rules and Rule Configuration for more details.

Anti-pattern

Aliasing the column to itself, where not necessary for changing the case of an identifier.

SELECT
    col AS col,
    "Col" AS "Col",
    COL AS col
FROM table;

Best practice

Not to use alias to rename the column to its original name. Self-aliasing leads to redundant code without changing any functionality, unless used to effectively change the case of the identifier.

SELECT
    col,
    "Col"
    COL,
FROM table;

-- Re-casing aliasing is still allowed where necessary, i.e.
SELECT
    col as "Col",
    "col" as "COL"
FROM table;

Ambiguous bundle¶

Code AM01¶

Rule ambiguous.distinct¶

Ambiguous use of `DISTINCT` in a `SELECT` statement with `GROUP BY`.¶

When using GROUP BY a DISTINCT` clause should not be necessary as every non-distinct SELECT clause must be included in the GROUP BY clause.

Name: ambiguous.distinct

Aliases: L021

Groups: all, core, ambiguous

Anti-pattern

DISTINCT and GROUP BY are conflicting.

SELECT DISTINCT
    a
FROM foo
GROUP BY a

Best practice

Remove DISTINCT or GROUP BY. In our case, removing GROUP BY is better.

SELECT DISTINCT
    a
FROM foo

Code AM02¶

Rule ambiguous.union¶

`UNION [DISTINCT|ALL]` is preferred over just `UNION`.¶

This rule is sqlfluff fix compatible.

Name: ambiguous.union

Aliases: L033

Groups: all, core, ambiguous

Note

This rule is only enabled for dialects that support UNION and UNION DISTINCT (ansi, bigquery, clickhouse, databricks, db2, hive, mysql, redshift, snowflake, and trino).

Anti-pattern

In this example, UNION DISTINCT should be preferred over UNION, because explicit is better than implicit.

SELECT a, b FROM table_1
UNION
SELECT a, b FROM table_2

Best practice

Specify DISTINCT or ALL after UNION (note that DISTINCT is the default behavior).

SELECT a, b FROM table_1
UNION DISTINCT
SELECT a, b FROM table_2

Code AM03¶

Rule ambiguous.order_by¶

Ambiguous ordering directions for columns in order by clause.¶

This rule is sqlfluff fix compatible.

Name: ambiguous.order_by

Aliases: L037

Groups: all, ambiguous

Anti-pattern

SELECT
    a, b
FROM foo
ORDER BY a, b DESC

Best practice

If any columns in the ORDER BY clause specify ASC or DESC, they should all do so.

SELECT
    a, b
FROM foo
ORDER BY a ASC, b DESC

Code AM04¶

Rule ambiguous.column_count¶

Query produces an unknown number of result columns.¶

Name: ambiguous.column_count

Aliases: L044

Groups: all, ambiguous

Anti-pattern

Querying all columns using * produces a query result where the number or ordering of columns changes if the upstream table’s schema changes. This should generally be avoided because it can cause slow performance, cause important schema changes to go undetected, or break production code. For example:

If a query does SELECT t.* and is expected to return columns a, b, and c, the actual columns returned will be wrong/different if columns are added to or deleted from the input table.
UNION and DIFFERENCE clauses require the inputs have the same number of columns (and compatible types).
JOIN queries may break due to new column name conflicts, e.g. the query references a column c which initially existed in only one input table but a column of the same name is added to another table.
CREATE TABLE (<<column schema>>) AS SELECT *

WITH cte AS (
    SELECT * FROM foo
)

SELECT * FROM cte
UNION
SELECT a, b FROM t

Best practice

Somewhere along the “path” to the source data, specify columns explicitly.

WITH cte AS (
    SELECT * FROM foo
)

SELECT a, b FROM cte
UNION
SELECT a, b FROM t

Code AM05¶

Rule ambiguous.join¶

Join clauses should be fully qualified.¶

By default this rule is configured to enforce fully qualified INNER JOIN clauses, but not [LEFT/RIGHT/FULL] OUTER JOIN. If you prefer a stricter lint then this is configurable.

This rule is sqlfluff fix compatible.

Name: ambiguous.join

Aliases: L051

Groups: all, ambiguous

Configuration

fully_qualify_join_types: Which types of JOIN clauses should be fully qualified? Must be one of ['inner', 'outer', 'both'].

Anti-pattern

A join is used without specifying the kind of join.

 SELECT
     foo
 FROM bar
 JOIN baz;

Best practice

Use INNER JOIN rather than JOIN.

 SELECT
     foo
 FROM bar
 INNER JOIN baz;

Code AM06¶

Rule ambiguous.column_references¶

Inconsistent column references in `GROUP BY/ORDER BY` clauses.¶

Name: ambiguous.column_references

Aliases: L054

Groups: all, core, ambiguous

Configuration

group_by_and_order_by_style: The expectation for using explicit column name references or implicit positional references. Must be one of ['consistent', 'implicit', 'explicit'].

Note

ORDER BY clauses from WINDOW clauses are ignored by this rule.

Anti-pattern

A mix of implicit and explicit column references are used in a GROUP BY clause.

 SELECT
     foo,
     bar,
     sum(baz) AS sum_value
 FROM fake_table
 GROUP BY
     foo, 2;

 -- The same also applies to column
 -- references in ORDER BY clauses.

 SELECT
     foo,
     bar
 FROM fake_table
 ORDER BY
     1, bar;

Best practice

Reference all GROUP BY/ORDER BY columns either by name or by position.

 -- GROUP BY: Explicit
 SELECT
     foo,
     bar,
     sum(baz) AS sum_value
 FROM fake_table
 GROUP BY
     foo, bar;

 -- ORDER BY: Explicit
 SELECT
     foo,
     bar
 FROM fake_table
 ORDER BY
     foo, bar;

 -- GROUP BY: Implicit
 SELECT
     foo,
     bar,
     sum(baz) AS sum_value
 FROM fake_table
 GROUP BY
     1, 2;

 -- ORDER BY: Implicit
 SELECT
     foo,
     bar
 FROM fake_table
 ORDER BY
     1, 2;

Code AM07¶

Rule ambiguous.set_columns¶

Queries within set query produce different numbers of columns.¶

Name: ambiguous.set_columns

Aliases: L068

Groups: all, ambiguous

Anti-pattern

When writing set expressions, all queries must return the same number of columns.

WITH cte AS (
    SELECT
        a,
        b
    FROM foo
)
SELECT * FROM cte
UNION
SELECT
    c,
    d,
    e
 FROM t

Best practice

Always specify columns when writing set queries and ensure that they all seleect same number of columns

WITH cte AS (
    SELECT a, b FROM foo
)
SELECT
    a,
    b
FROM cte
UNION
SELECT
    c,
    d
FROM t

Code AM08¶

Rule ambiguous.join_condition¶

Implicit cross join detected.¶

This rule is sqlfluff fix compatible.

Name: ambiguous.join_condition

Groups: all, ambiguous

Anti-pattern

Cross joins are valid, but rare in the wild - and more often created by mistake than on purpose. This rule catches situations where a cross join has been specified, but not explicitly and so the risk of a mistaken cross join is highly likely.

 SELECT
     foo
 FROM bar
 JOIN baz;

Best practice

Use CROSS JOIN.

 SELECT
     foo
 FROM bar
 CROSS JOIN baz;

Capitalisation bundle¶

Code CP01¶

Rule capitalisation.keywords¶

Inconsistent capitalisation of keywords.¶

This rule is sqlfluff fix compatible.

Name: capitalisation.keywords

Aliases: L010

Groups: all, core, capitalisation

Configuration

capitalisation_policy: The capitalisation policy to enforce. Must be one of ['consistent', 'upper', 'lower', 'capitalise'].
ignore_words: Comma separated list of words to ignore from rule.
ignore_words_regex: Words to ignore from rule if they are a partial match for the regular expression. To ignore only full matches you can use ^ (beginning of text) and $ (end of text). Due to regular expression operator precedence, it is good practice to use parentheses around everything between ^ and $.

Anti-pattern

In this example, select is in lower-case whereas FROM is in upper-case.

select
    a
FROM foo

Best practice

Make all keywords either in upper-case or in lower-case.

SELECT
    a
FROM foo

-- Also good

select
    a
from foo

Code CP02¶

Rule capitalisation.identifiers¶

Inconsistent capitalisation of unquoted identifiers.¶

This rule applies to all unquoted identifiers, whether references or aliases, and whether they refer to columns or other objects (such as tables or schemas).

This rule is sqlfluff fix compatible.

Name: capitalisation.identifiers

Aliases: L014

Groups: all, core, capitalisation

Configuration

extended_capitalisation_policy: The capitalisation policy to enforce, extended with PascalCase, snake_case, and camelCase. This is separate from capitalisation_policy as it should not be applied to keywords.Camel, Pascal, and Snake will never be inferred when the policy is set to consistent. This is because snake can cause destructive changes to the identifier, and unlinted code is too easily mistaken for camel and pascal. If, when set to consistent, no consistent case is found, it will default to upper. Must be one of ['consistent', 'upper', 'lower', 'pascal', 'capitalise', 'snake', 'camel'].
ignore_words: Comma separated list of words to ignore from rule.
ignore_words_regex: Words to ignore from rule if they are a partial match for the regular expression. To ignore only full matches you can use ^ (beginning of text) and $ (end of text). Due to regular expression operator precedence, it is good practice to use parentheses around everything between ^ and $.
unquoted_identifiers_policy: Types of unquoted identifiers to flag violations for. Must be one of ['all', 'aliases', 'column_aliases', 'table_aliases'].

Note

In most dialects, unquoted identifiers are treated as case-insensitive and so the fixes proposed by this rule do not change the interpretation of the query. HOWEVER, some databases (notably Google BigQuery, Trino and ClickHouse) do take the casing of unquoted identifiers into account when determining the casing of the column heading in the result.

As this feature is only present in a few dialects, and not widely understood by users, we regard it as an antipattern. It is more widely understood that if the case of an identifier matters, then it should be quoted. If you, or your organisation, do wish to rely on this feature, we recommend that you disabled this rule (see Enabling and Disabling Rules).

Anti-pattern

In this example, unquoted identifier a is in lower-case but B is in upper-case.

select
    a,
    B
from foo

In this more complicated example, there are a mix of capitalisations in both reference and aliases of columns and tables. That inconsistency is acceptable when those identifiers are quoted, but not when unquoted.

select
    col_1 + Col_2 as COL_3,
    "COL_4" as Col_5
from Foo as BAR

Best practice

Ensure all unquoted identifiers are either in upper-case or in lower-case.

select
    a,
    b
from foo;

-- ...also good...

select
    A,
    B
from foo;

--- ...or for comparison with our more complex example, this too:

select
    col_1 + col_2 as col_3,
    "COL_4" as col_5
from foo as bar

Code CP03¶

Rule capitalisation.functions¶

Inconsistent capitalisation of function names.¶

This rule is sqlfluff fix compatible.

Name: capitalisation.functions

Aliases: L030

Groups: all, core, capitalisation

Configuration

extended_capitalisation_policy: The capitalisation policy to enforce, extended with PascalCase, snake_case, and camelCase. This is separate from capitalisation_policy as it should not be applied to keywords.Camel, Pascal, and Snake will never be inferred when the policy is set to consistent. This is because snake can cause destructive changes to the identifier, and unlinted code is too easily mistaken for camel and pascal. If, when set to consistent, no consistent case is found, it will default to upper. Must be one of ['consistent', 'upper', 'lower', 'pascal', 'capitalise', 'snake', 'camel'].
ignore_words: Comma separated list of words to ignore from rule.
ignore_words_regex: Words to ignore from rule if they are a partial match for the regular expression. To ignore only full matches you can use ^ (beginning of text) and $ (end of text). Due to regular expression operator precedence, it is good practice to use parentheses around everything between ^ and $.

Anti-pattern

In this example, the two SUM functions don’t have the same capitalisation.

SELECT
    sum(a) AS aa,
    SUM(b) AS bb
FROM foo

Best practice

Make the case consistent.

SELECT
    sum(a) AS aa,
    sum(b) AS bb
FROM foo

Code CP04¶

Rule capitalisation.literals¶

Inconsistent capitalisation of boolean/null literal.¶

This rule is sqlfluff fix compatible.

Name: capitalisation.literals

Aliases: L040

Groups: all, core, capitalisation

Configuration

capitalisation_policy: The capitalisation policy to enforce. Must be one of ['consistent', 'upper', 'lower', 'capitalise'].
ignore_words: Comma separated list of words to ignore from rule.
ignore_words_regex: Words to ignore from rule if they are a partial match for the regular expression. To ignore only full matches you can use ^ (beginning of text) and $ (end of text). Due to regular expression operator precedence, it is good practice to use parentheses around everything between ^ and $.

Anti-pattern

In this example, null and false are in lower-case whereas TRUE is in upper-case.

select
    a,
    null,
    TRUE,
    false
from foo

Best practice

Ensure all literal null/true/false literals are consistently upper or lower case

select
    a,
    NULL,
    TRUE,
    FALSE
from foo

-- Also good

select
    a,
    null,
    true,
    false
from foo

Code CP05¶

Rule capitalisation.types¶

Inconsistent capitalisation of datatypes.¶

This rule is sqlfluff fix compatible.

Name: capitalisation.types

Aliases: L063

Groups: all, core, capitalisation

Configuration

extended_capitalisation_policy: The capitalisation policy to enforce, extended with PascalCase, snake_case, and camelCase. This is separate from capitalisation_policy as it should not be applied to keywords.Camel, Pascal, and Snake will never be inferred when the policy is set to consistent. This is because snake can cause destructive changes to the identifier, and unlinted code is too easily mistaken for camel and pascal. If, when set to consistent, no consistent case is found, it will default to upper. Must be one of ['consistent', 'upper', 'lower', 'pascal', 'capitalise', 'snake', 'camel'].
ignore_words: Comma separated list of words to ignore from rule.
ignore_words_regex: Words to ignore from rule if they are a partial match for the regular expression. To ignore only full matches you can use ^ (beginning of text) and $ (end of text). Due to regular expression operator precedence, it is good practice to use parentheses around everything between ^ and $.

Anti-pattern

In this example, int and unsigned are in lower-case whereas VARCHAR is in upper-case.

CREATE TABLE t (
    a int unsigned,
    b VARCHAR(15)
);

Best practice

Ensure all datatypes are consistently upper or lower case

CREATE TABLE t (
    a INT UNSIGNED,
    b VARCHAR(15)
);

Convention bundle¶

Code CV01¶

Rule convention.not_equal¶

Consistent usage of `!=` or `<>` for “not equal to” operator.¶

This rule is sqlfluff fix compatible.

Name: convention.not_equal

Aliases: L061

Groups: all, convention

Configuration

preferred_not_equal_style: The style for using not equal to operator. Defaults to consistent. Must be one of ['consistent', 'c_style', 'ansi'].

Anti-pattern

SELECT * FROM X WHERE 1 <> 2 AND 3 != 4;

Best practice

Ensure all “not equal to” comparisons are consistent, not mixing != and <>.

SELECT * FROM X WHERE 1 != 2 AND 3 != 4;

Code CV02¶

Rule convention.coalesce¶

Use `COALESCE` instead of `IFNULL` or `NVL`.¶

This rule is sqlfluff fix compatible.

Name: convention.coalesce

Aliases: L060

Groups: all, convention

Anti-pattern

IFNULL or NVL are used to fill NULL values.

SELECT ifnull(foo, 0) AS bar,
FROM baz;

SELECT nvl(foo, 0) AS bar,
FROM baz;

Best practice

Use COALESCE instead. COALESCE is universally supported, whereas Redshift doesn’t support IFNULL and BigQuery doesn’t support NVL. Additionally, COALESCE is more flexible and accepts an arbitrary number of arguments.

SELECT coalesce(foo, 0) AS bar,
FROM baz;

Code CV03¶

Rule convention.select_trailing_comma¶

Trailing commas within select clause.¶

This rule is sqlfluff fix compatible.

Name: convention.select_trailing_comma

Aliases: L038

Groups: all, core, convention

Configuration

select_clause_trailing_comma: Should trailing commas within select clauses be required or forbidden? Must be one of ['forbid', 'require'].

Note

For many database backends this is allowed. For some users this may be something they wish to enforce (in line with Python best practice). Many database backends regard this as a syntax error, and as such the SQLFluff default is to forbid trailing commas in the select clause.

Anti-pattern

SELECT
    a,
    b,
FROM foo

Best practice

SELECT
    a,
    b
FROM foo

Code CV04¶

Rule convention.count_rows¶

Use consistent syntax to express “count number of rows”.¶

Note:: If both prefer_count_1 and prefer_count_0 are set to true then prefer_count_1 has precedence.

COUNT(*), COUNT(1), and even COUNT(0) are equivalent syntaxes in many SQL engines due to optimizers interpreting these instructions as “count number of rows in result”.

The ANSI-92 spec mentions the COUNT(*) syntax specifically as having a special meaning:

If COUNT(*) is specified, then the result is the cardinality of T.

So by default, SQLFluff enforces the consistent use of COUNT(*).

If the SQL engine you work with, or your team, prefers COUNT(1) or COUNT(0) over COUNT(*), you can configure this rule to consistently enforce your preference.

This rule is sqlfluff fix compatible.

Name: convention.count_rows

Aliases: L047

Groups: all, core, convention

Configuration

prefer_count_0: Should count(0) be preferred over count(*) and count(1)? Must be one of [True, False].
prefer_count_1: Should count(1) be preferred over count(*) and count(0)? Must be one of [True, False].

Anti-pattern

select
    count(1)
from table_a

Best practice

Use count(*) unless specified otherwise by config prefer_count_1, or prefer_count_0 as preferred.

select
    count(*)
from table_a

Code CV05¶

Rule convention.is_null¶

Comparisons with NULL should use “IS” or “IS NOT”.¶

This rule is sqlfluff fix compatible.

Name: convention.is_null

Aliases: L049

Groups: all, core, convention

Anti-pattern

In this example, the = operator is used to check for NULL values.

SELECT
    a
FROM foo
WHERE a = NULL

Best practice

Use IS or IS NOT to check for NULL values.

SELECT
    a
FROM foo
WHERE a IS NULL

Code CV06¶

Rule convention.terminator¶

Statements must end with a semi-colon.¶

This rule is sqlfluff fix compatible.

Name: convention.terminator

Aliases: L052

Groups: all, convention

Configuration

multiline_newline: Should semi-colons be placed on a new line after multi-line statements? Must be one of [True, False].
require_final_semicolon: Should final semi-colons be required? (N.B. forcing trailing semi-colons is not recommended for dbt users as it can cause issues when wrapping the query within other SQL queries). Must be one of [True, False].

Anti-pattern

A statement is not immediately terminated with a semi-colon. The • represents space.

 SELECT
     a
 FROM foo

 ;

 SELECT
     b
 FROM bar••;

Best practice

Immediately terminate the statement with a semi-colon.

 SELECT
     a
 FROM foo;

Code CV07¶

Rule convention.statement_brackets¶

Top-level statements should not be wrapped in brackets.¶

This rule is sqlfluff fix compatible.

Name: convention.statement_brackets

Aliases: L053

Groups: all, convention

Anti-pattern

A top-level statement is wrapped in brackets.

 (SELECT
     foo
 FROM bar)

 -- This also applies to statements containing a sub-query.

 (SELECT
     foo
 FROM (SELECT * FROM bar))

Best practice

Don’t wrap top-level statements in brackets.

 SELECT
     foo
 FROM bar

 -- Likewise for statements containing a sub-query.

 SELECT
     foo
 FROM (SELECT * FROM bar)

Code CV08¶

Rule convention.left_join¶

Use `LEFT JOIN` instead of `RIGHT JOIN`.¶

Name: convention.left_join

Aliases: L055

Groups: all, convention

Anti-pattern

RIGHT JOIN is used.

 SELECT
     foo.col1,
     bar.col2
 FROM foo
 RIGHT JOIN bar
     ON foo.bar_id = bar.id;

Best practice

Refactor and use LEFT JOIN instead.

 SELECT
     foo.col1,
     bar.col2
 FROM bar
 LEFT JOIN foo
     ON foo.bar_id = bar.id;

Code CV09¶

Rule convention.blocked_words¶

Block a list of configurable words from being used.¶

This generic rule can be useful to prevent certain keywords, functions, or objects from being used. Only whole words can be blocked, not phrases, nor parts of words.

This block list is case insensitive.

Example use cases

We prefer BOOL over BOOLEAN and there is no existing rule to enforce this. Until such a rule is written, we can add BOOLEAN to the deny list to cause a linting error to flag this.
We have deprecated a schema/table/function and want to prevent it being used in future. We can add that to the denylist and then add a -- noqa: CV09 for the few exceptions that still need to be in the code base for now.

Name: convention.blocked_words

Aliases: L062

Groups: all, convention

Configuration

blocked_regex: Optional, regex of blocked pattern which should not be used in statements.
blocked_words: Optional, comma-separated list of blocked words which should not be used in statements.
match_source: Optional, also match regex of blocked pattern before applying templating.

Anti-pattern

If the blocked_words config is set to deprecated_table,bool then the following will flag:

SELECT * FROM deprecated_table WHERE 1 = 1;
CREATE TABLE myschema.t1 (a BOOL);

Best practice

Do not used any blocked words:

SELECT * FROM another_table WHERE 1 = 1;
CREATE TABLE myschema.t1 (a BOOLEAN);

Code CV10¶

Rule convention.quoted_literals¶

Consistent usage of preferred quotes for quoted literals.¶

Some databases allow quoted literals to use either single or double quotes. Prefer one type of quotes as specified in rule setting, falling back to alternate quotes to reduce the need for escapes.

Dollar-quoted raw strings are excluded from this rule, as they are mostly used for literal UDF Body definitions.

This rule is sqlfluff fix compatible.

Name: convention.quoted_literals

Aliases: L064

Groups: all, convention

Configuration

force_enable: Run this rule even for dialects where this rule is disabled by default. Must be one of [True, False].
preferred_quoted_literal_style: Preferred quoting style to use for the quoted literals. If set to consistent quoting style is derived from the first quoted literalin the file. Must be one of ['consistent', 'single_quotes', 'double_quotes'].

Note

This rule only checks quoted literals and not quoted identifiers as they often cannot interchange single and double quotes

This rule is only enabled for dialects that allow single and double quotes for quoted literals (currently bigquery, databricks, hive, mysql, sparksql). It can be enabled for other dialects with the force_enable = True flag.

Anti-pattern

 select
     "abc",
     'abc',
     "\"",
     "abc" = 'abc'
 from foo

Best practice

Ensure all quoted literals use preferred quotes, unless escaping can be reduced by using alternate quotes.

 select
     "abc",
     "abc",
     '"',
     "abc" = "abc"
 from foo

Code CV11¶

Rule convention.casting_style¶

Enforce consistent type casting style.¶

This rule is sqlfluff fix compatible.

Name: convention.casting_style

Aliases: L067

Groups: all, convention

Configuration

preferred_type_casting_style: The expectation for using sql type casting. Must be one of ['consistent', 'shorthand', 'convert', 'cast'].

Note

This is only compatible with 2-arguments CONVERT as some dialects allow an optional 3rd argument e.g TSQL, which cannot be rewritten into CAST. This rule is disabled by default for Teradata because it supports different type casting apart from CONVERT and :: e.g DATE ‘2007-01-01’, ‘9999-12-31’ (DATE).

Anti-pattern

Using mixture of CONVERT, :: and CAST when preferred_type_casting_style config is set to consistent (default).

SELECT
    CONVERT(int, 1) AS bar,
    100::int::text,
    CAST(10 AS text) AS coo
FROM foo;

Best practice

Use consistent type casting style.

SELECT
    CAST(1 AS int) AS bar,
    CAST(CAST(100 AS int) AS text),
    CAST(10 AS text) AS coo
FROM foo;

Code CV12¶

Rule convention.join_condition¶

Use JOIN … ON … instead of WHERE … for join conditions.¶

This rule is sqlfluff fix compatible.

Name: convention.join_condition

Groups: all, convention

Anti-pattern

Using WHERE clause for join conditions.

SELECT
    foo.a
    , bar.b
FROM foo
JOIN bar
WHERE foo.x = bar.y;

Best practice

Use JOIN ON clause for join condition.

SELECT
    foo.a
    , bar.b
FROM foo
JOIN bar
ON foo.x = bar.y;

Jinja bundle¶

Code JJ01¶

Rule jinja.padding¶

Jinja tags should have a single whitespace on either side.¶

This rule is only active if the jinja templater (or one of it’s subclasses, like the dbt templater) are used for the current file.

This rule is sqlfluff fix compatible.

Name: jinja.padding

Aliases: L046

Groups: all, core, jinja

Anti-pattern

Jinja tags with either no whitespace or very long whitespace are hard to read.

 SELECT {{    a     }} from {{ref('foo')}}

Best practice

A single whitespace surrounding Jinja tags, alternatively longer gaps containing newlines are acceptable.

 SELECT {{ a }} from {{ ref('foo') }};
 SELECT {{ a }} from {{
     ref('foo')
 }};

Layout bundle¶

Code LT01¶

Rule layout.spacing¶

Inappropriate Spacing.¶

This rule checks for an enforces the spacing as configured in Configuring Layout. This includes excessive whitespace, trailing whitespace at the end of a line and also the wrong spacing between elements on the line. Because of this wide reach you may find that you wish to add specific configuration in your project to tweak how specific elements are treated. Rather than configuration on this specific rule, use the sqlfluff.layout section of your configuration file to customise how this rule operates.

The • character represents a space in the examples below.

This rule is sqlfluff fix compatible.

Name: layout.spacing

Aliases: L001, L005, L006, L008, L023, L024, L039, L048, L071

Groups: all, core, layout

Anti-pattern

SELECT
    a,        b(c) as d••
FROM foo••••
JOIN bar USING(a)

Best practice

Unless an indent or preceding a comment, whitespace should be a single space.
There should also be no trailing whitespace at the ends of lines.
There should be a space after USING so that it’s not confused for a function.

SELECT
    a, b(c) as d
FROM foo
JOIN bar USING (a)

Code LT02¶

Rule layout.indent¶

Incorrect Indentation.¶

This rule is sqlfluff fix compatible.

Name: layout.indent

Aliases: L002, L003, L004

Groups: all, core, layout

Anti-pattern

The • character represents a space and the → character represents a tab. In this example, the third line contains five spaces instead of four and the second line contains two spaces and one tab.

 SELECT
 ••→a,
 •••••b
 FROM foo

Best practice

Change the indentation to use a multiple of four spaces. This example also assumes that the indent_unit config value is set to space. If it had instead been set to tab, then the indents would be tabs instead.

 SELECT
 ••••a,
 ••••b
 FROM foo

Code LT03¶

Rule layout.operators¶

Operators should follow a standard for being before/after newlines.¶

The configuration for whether operators should be trailing or leading is part of Configuring Layout. The default configuration is:

[sqlfluff:layout:type:binary_operator]
line_position = leading

[sqlfluff:layout:type:comparison_operator]
line_position = leading

This rule is sqlfluff fix compatible.

Name: layout.operators

Aliases: L007

Groups: all, layout

Anti-pattern

In this example, if line_position = leading (or unspecified, as is the default), then the operator + should not be at the end of the second line.

SELECT
    a +
    b
FROM foo

Best practice

If line_position = leading (or unspecified, as this is the default), place the operator after the newline.

SELECT
    a
    + b
FROM foo

If line_position = trailing, place the operator before the newline.

SELECT
    a +
    b
FROM foo

Code LT04¶

Rule layout.commas¶

Leading/Trailing comma enforcement.¶

The configuration for whether operators should be trailing or leading is part of Configuring Layout. The default configuration is:

[sqlfluff:layout:type:comma]
line_position = trailing

This rule is sqlfluff fix compatible.

Name: layout.commas

Aliases: L019

Groups: all, layout

Anti-pattern

There is a mixture of leading and trailing commas.

SELECT
    a
    , b,
    c
FROM foo

Best practice

By default, SQLFluff prefers trailing commas. However it is configurable for leading commas. The chosen style must be used consistently throughout your SQL.

SELECT
    a,
    b,
    c
FROM foo

-- Alternatively, set the configuration file to 'leading'
-- and then the following would be acceptable:

SELECT
    a
    , b
    , c
FROM foo

Code LT05¶

Rule layout.long_lines¶

Line is too long.¶

This rule is sqlfluff fix compatible.

Name: layout.long_lines

Aliases: L016

Groups: all, core, layout

Configuration

ignore_comment_clauses: Should comment clauses (e.g. column comments) be ignored when linting line lengths? Must be one of [True, False].
ignore_comment_lines: Should lines that contain only whitespace and comments be ignored when linting line lengths? Must be one of [True, False].

Code LT06¶

Rule layout.functions¶

Function name not immediately followed by parenthesis.¶

This rule is sqlfluff fix compatible.

Name: layout.functions

Aliases: L017

Groups: all, core, layout

Anti-pattern

In this example, there is a space between the function and the parenthesis.

SELECT
    sum (a)
FROM foo

Best practice

Remove the space between the function and the parenthesis.

SELECT
    sum(a)
FROM foo

Code LT07¶

Rule layout.cte_bracket¶

`WITH` clause closing bracket should be on a new line.¶

This rule is sqlfluff fix compatible.

Name: layout.cte_bracket

Aliases: L018

Groups: all, core, layout

Anti-pattern

In this example, the closing bracket is on the same line as CTE.

 WITH zoo AS (
     SELECT a FROM foo)

 SELECT * FROM zoo

Best practice

Move the closing bracket on a new line.

WITH zoo AS (
    SELECT a FROM foo
)

SELECT * FROM zoo

Code LT08¶

Rule layout.cte_newline¶

Blank line expected but not found after CTE closing bracket.¶

This rule is sqlfluff fix compatible.

Name: layout.cte_newline

Aliases: L022

Groups: all, core, layout

Anti-pattern

There is no blank line after the CTE closing bracket. In queries with many CTEs, this hinders readability.

WITH plop AS (
    SELECT * FROM foo
)
SELECT a FROM plop

Best practice

Add a blank line.

WITH plop AS (
    SELECT * FROM foo
)

SELECT a FROM plop

Code LT09¶

Rule layout.select_targets¶

Select targets should be on a new line unless there is only one select target.¶

This rule is sqlfluff fix compatible.

Name: layout.select_targets

Aliases: L036

Groups: all, layout

Configuration

wildcard_policy: Treatment of wildcards. Defaults to single. Must be one of ['single', 'multiple'].

Note

By default, a wildcard (e.g. SELECT *) is considered a single select target. If you want it to be treated as multiple select targets, configure wildcard_policy = multiple.

Anti-pattern

Multiple select targets on the same line.

select a, b
from foo;

-- Single select target on its own line.

SELECT
    a
FROM foo;

Best practice

Multiple select targets each on their own line.

select
    a,
    b
from foo;

-- Single select target on the same line as the ``SELECT``
-- keyword.

SELECT a
FROM foo;

-- When select targets span multiple lines, however they
-- can still be on a new line.

SELECT
    SUM(
        1 + SUM(
            2 + 3
        )
    ) AS col
FROM test_table;

Code LT10¶

Rule layout.select_modifiers¶

`SELECT` modifiers (e.g. `DISTINCT`) must be on the same line as `SELECT`.¶

This rule is sqlfluff fix compatible.

Name: layout.select_modifiers

Aliases: L041

Groups: all, core, layout

Anti-pattern

select
    distinct a,
    b
from x

Best practice

select distinct
    a,
    b
from x

Code LT11¶

Rule layout.set_operators¶

Set operators should be surrounded by newlines.¶

This rule is sqlfluff fix compatible.

Name: layout.set_operators

Aliases: L065

Groups: all, core, layout

Anti-pattern

In this example, UNION ALL is not on a line itself.

SELECT 'a' AS col UNION ALL
SELECT 'b' AS col

Best practice

SELECT 'a' AS col
UNION ALL
SELECT 'b' AS col

Code LT12¶

Rule layout.end_of_file¶

Files must end with a single trailing newline.¶

This rule is sqlfluff fix compatible.

Name: layout.end_of_file

Aliases: L009, layout.end-of-file

Groups: all, core, layout

Anti-pattern

The content in file does not end with a single trailing newline. The $ represents end of file.

 SELECT
     a
 FROM foo$

 -- Ending on an indented line means there is no newline
 -- at the end of the file, the • represents space.

 SELECT
 ••••a
 FROM
 ••••foo
 ••••$

 -- Ending on a semi-colon means the last line is not a
 -- newline.

 SELECT
     a
 FROM foo
 ;$

 -- Ending with multiple newlines.

 SELECT
     a
 FROM foo

 $

Best practice

Add trailing newline to the end. The $ character represents end of file.

 SELECT
     a
 FROM foo
 $

 -- Ensuring the last line is not indented so is just a
 -- newline.

 SELECT
 ••••a
 FROM
 ••••foo
 $

 -- Even when ending on a semi-colon, ensure there is a
 -- newline after.

 SELECT
     a
 FROM foo
 ;
 $

Code LT13¶

Rule layout.start_of_file¶

Files must not begin with newlines or whitespace.¶

This rule is sqlfluff fix compatible.

Name: layout.start_of_file

Aliases: L050

Groups: all, layout

Anti-pattern

The file begins with newlines or whitespace. The ^ represents the beginning of the file.

 ^

 SELECT
     a
 FROM foo

 -- Beginning on an indented line is also forbidden,
 -- (the • represents space).

 ••••SELECT
 ••••a
 FROM
 ••••foo

Best practice

Start file on either code or comment. (The ^ represents the beginning of the file.)

 ^SELECT
     a
 FROM foo

 -- Including an initial block comment.

 ^/*
 This is a description of my SQL code.
 */
 SELECT
     a
 FROM
     foo

 -- Including an initial inline comment.

 ^--This is a description of my SQL code.
 SELECT
     a
 FROM
     foo

Code LT14¶

Rule layout.keyword_newline¶

Keyword clauses should follow a standard for being before/after newlines.¶

This rule is sqlfluff fix compatible.

Name: layout.keyword_newline

Groups: all, layout

Anti-pattern

In this example, the keyword are not at the beginning of or alone on the line.

SELECT 'a' AS col FROM tab WHERE x = 4 ORDER BY y LIMIT 5

Best practice

SELECT 'a' AS col
FROM tab
WHERE x = 4
ORDER BY y
LIMIT 5

SELECT 'a' AS col
FROM
    tab
WHERE
    x = 4
ORDER BY
    y
LIMIT
    5

References bundle¶

Code RF01¶

Rule references.from¶

References cannot reference objects not present in `FROM` clause.¶

Name: references.from

Aliases: L026

Groups: all, core, references

Configuration

force_enable: Run this rule even for dialects where this rule is disabled by default. Must be one of [True, False].

Note

This rule is disabled by default for BigQuery, Databricks, Hive, Redshift, SOQL and SparkSQL due to the support of things like structs and lateral views which trigger false positives. It can be enabled with the force_enable = True flag.

Anti-pattern

In this example, the reference vee has not been declared.

SELECT
    vee.a
FROM foo

Best practice

Remove the reference.

SELECT
    a
FROM foo

Code RF02¶

Rule references.qualification¶

References should be qualified if select has more than one referenced table/view.¶

Name: references.qualification

Aliases: L027

Groups: all, references

Note

Except if they’re present in a USING clause.

Anti-pattern

In this example, the reference vee has not been declared, and the variables a and b are potentially ambiguous.

SELECT a, b
FROM foo
LEFT JOIN vee ON vee.a = foo.a

Best practice

Add the references.

SELECT foo.a, vee.b
FROM foo
LEFT JOIN vee ON vee.a = foo.a

Code RF03¶

Rule references.consistent¶

Column references should be qualified consistently in single table statements.¶

This rule is sqlfluff fix compatible.

Name: references.consistent

Aliases: L028

Groups: all, references

Configuration

force_enable: Run this rule even for dialects where this rule is disabled by default. Must be one of [True, False].
single_table_references: The expectation for references in single-table select. Must be one of ['consistent', 'qualified', 'unqualified'].

Note

For BigQuery, Hive and Redshift this rule is disabled by default. This is due to historical false positives associated with STRUCT data types. This default behaviour may be changed in the future. The rule can be enabled with the force_enable = True flag.

“consistent” will be fixed to “qualified” if inconsistency is found.

Anti-pattern

In this example, only the reference to b is qualified.

SELECT
    a,
    foo.b
FROM foo

Best practice

Either all column references should be qualified, or all unqualified.

SELECT
    a,
    b
FROM foo

-- Also good

SELECT
    foo.a,
    foo.b
FROM foo

Code RF04¶

Rule references.keywords¶

Keywords should not be used as identifiers.¶

Although unreserved keywords can be used as identifiers, and reserved words can be used as quoted identifiers, best practice is to avoid where possible, to avoid any misunderstandings as to what the alias represents.

Name: references.keywords

Aliases: L029

Groups: all, references

Configuration

ignore_words: Comma separated list of words to ignore from rule.
ignore_words_regex: Words to ignore from rule if they are a partial match for the regular expression. To ignore only full matches you can use ^ (beginning of text) and $ (end of text). Due to regular expression operator precedence, it is good practice to use parentheses around everything between ^ and $.
quoted_identifiers_policy: Types of quoted identifiers to flag violations for. Must be one of ['all', 'aliases', 'column_aliases', 'table_aliases', 'none'].
unquoted_identifiers_policy: Types of unquoted identifiers to flag violations for. Must be one of ['all', 'aliases', 'column_aliases', 'table_aliases'].

Note

Note that reserved keywords cannot be used as unquoted identifiers and will cause parsing errors and so are not covered by this rule.

Anti-pattern

In this example, SUM (built-in function) is used as an alias.

SELECT
    sum.a
FROM foo AS sum

Best practice

Avoid keywords as the name of an alias.

SELECT
    vee.a
FROM foo AS vee

Code RF05¶

Rule references.special_chars¶

Do not use special characters in identifiers.¶

Name: references.special_chars

Aliases: L057

Groups: all, references

Configuration

additional_allowed_characters: Optional list of extra allowed characters, in addition to alphanumerics (A-Z, a-z, 0-9) and underscores.
allow_space_in_identifier: Should spaces in identifiers be allowed? Must be one of [True, False].
ignore_words: Comma separated list of words to ignore from rule.
ignore_words_regex: Words to ignore from rule if they are a partial match for the regular expression. To ignore only full matches you can use ^ (beginning of text) and $ (end of text). Due to regular expression operator precedence, it is good practice to use parentheses around everything between ^ and $.
quoted_identifiers_policy: Types of quoted identifiers to flag violations for. Must be one of ['all', 'aliases', 'column_aliases', 'table_aliases', 'none'].
unquoted_identifiers_policy: Types of unquoted identifiers to flag violations for. Must be one of ['all', 'aliases', 'column_aliases', 'table_aliases'].

Anti-pattern

Using special characters within identifiers when creating or aliasing objects.

CREATE TABLE DBO.ColumnNames
(
    [Internal Space] INT,
    [Greater>Than] INT,
    [Less<Than] INT,
    Number# INT
)

Best practice

Identifiers should include only alphanumerics and underscores.

CREATE TABLE DBO.ColumnNames
(
    [Internal_Space] INT,
    [GreaterThan] INT,
    [LessThan] INT,
    NumberVal INT
)

Code RF06¶

Rule references.quoting¶

Unnecessary quoted identifier.¶

This rule will fail if the quotes used to quote an identifier are (un)necessary depending on the force_quote_identifier configuration. This rule applies to both column references and their aliases. The default (safe) behaviour is designed not to unexpectedly corrupt SQL. That means the circumstances in which quotes can be safely removed depends on the current dialect would resolve the unquoted variant of the identifier (see below for examples).

Additionally this rule may be configured to a more aggressive setting by setting case_sensitive to False, in which case quotes will be removed regardless of the casing of the contained identifier. Any identifiers which contain special characters, spaces or keywords will still be left quoted. This setting is more appropriate for projects or teams where there is more control over the inputs and outputs of queries, and where it’s more viable to institute rules such as enforcing that all identifiers are the default casing (and therefore meaning that using quotes to change the case of identifiers is unnecessary).

Dialect group	✅ Example where quotes are safe to remove.	⚠️ Examples where quotes are not safe to remove.
Natively `UPPERCASE` dialects e.g. Snowflake, BigQuery, TSQL & Oracle.	Identifiers which, without quotes, would resolve to the default casing of `FOO` i.e. `"FOO"`.	Identifiers where the quotes are necessary to preserve case (e.g. `"Foo"` or `"foo"`), or where the identifier contains something invalid without the quotes such as keywords or special characters e.g. `"SELECT"`, `"With Space"` or `"Special&Characters"`.
Natively `lowercase` dialects e.g. Athena, Hive & Postgres	Identifiers which, without quotes, would resolve to the default casing of `foo` i.e. `"foo"`.	Identifiers where the quotes are necessary to preserve case (e.g. `"Foo"` or `"foo"`), or where the identifier contains something invalid without the quotes such as keywords or special characters e.g. `"SELECT"`, `"With Space"` or `"Special&Characters"`.
Case insensitive dialects e.g. DuckDB or Apache Spark SQL	Any identifiers which are valid without quotes: e.g. `"FOO"`, `"foo"`, `"Foo"`, `"fOo"`, `FOO` and `foo` would all resolve to the same object.	Identifiers which contain something invalid without the quotes such as keywords or special characters e.g. `"SELECT"`, `"With Space"` or `"Special&Characters"`.

This rule is closely associated with (and constrained by the same above factors) as aliasing.self_alias.column (AL09).

When prefer_quoted_identifiers = False (default behaviour), the quotes are unnecessary, except for reserved keywords and special characters in identifiers.

This rule is sqlfluff fix compatible.

Name: references.quoting

Aliases: L059

Groups: all, references

Configuration

case_sensitive: If False, comparison is done case in-sensitively. Defaults to True. Must be one of [True, False].
ignore_words: Comma separated list of words to ignore from rule.
ignore_words_regex: Words to ignore from rule if they are a partial match for the regular expression. To ignore only full matches you can use ^ (beginning of text) and $ (end of text). Due to regular expression operator precedence, it is good practice to use parentheses around everything between ^ and $.
prefer_quoted_identifiers: If True, requires every identifier to be quoted. Defaults to False. Must be one of [True, False].
prefer_quoted_keywords: If True, requires every keyword used as an identifier to be quoted. Defaults to False. Must be one of [True, False].

Anti-pattern

In this example, valid unquoted identifiers, that are not also reserved keywords, are needlessly quoted.

SELECT "foo" as "bar";  -- For lowercase dialects like Postgres
SELECT "FOO" as "BAR";  -- For uppercase dialects like Snowflake

Best practice

Use unquoted identifiers where possible.

SELECT foo as bar;  -- For lowercase dialects like Postgres
SELECT FOO as BAR;  -- For uppercase dialects like Snowflake

-- Note that where the case of the quoted identifier requires
-- the quotes to remain, or where the identifier cannot be
-- unquoted because it would be invalid to do so, the quotes
-- may remain. For example:
SELECT
    "Case_Sensitive_Identifier" as is_allowed,
    "Identifier with spaces or speci@l characters" as this_too,
    "SELECT" as also_reserved_words
FROM "My Table With Spaces"

When prefer_quoted_identifiers = True, the quotes are always necessary, no matter if the identifier is valid, a reserved keyword, or contains special characters.

Note

Note due to different quotes being used by different dialects supported by SQLFluff, and those quotes meaning different things in different contexts, this mode is not sqlfluff fix compatible.

Anti-pattern

In this example, a valid unquoted identifier, that is also not a reserved keyword, is required to be quoted.

SELECT 123 as foo

Best practice Use quoted identifiers.

SELECT 123 as "foo" -- For ANSI, ...
-- or
SELECT 123 as `foo` -- For BigQuery, MySql, ...

Structure bundle¶

Code ST01¶

Rule structure.else_null¶

Do not specify `else null` in a case when statement (redundant).¶

This rule is sqlfluff fix compatible.

Name: structure.else_null

Aliases: L035

Groups: all, structure

Anti-pattern

select
    case
        when name like '%cat%' then 'meow'
        when name like '%dog%' then 'woof'
        else null
    end
from x

Best practice

Omit else null

select
    case
        when name like '%cat%' then 'meow'
        when name like '%dog%' then 'woof'
    end
from x

Code ST02¶

Rule structure.simple_case¶

Unnecessary `CASE` statement.¶

This rule is sqlfluff fix compatible.

Name: structure.simple_case

Aliases: L043

Groups: all, structure

Anti-pattern

CASE statement returns booleans.

select
    case
        when fab > 0 then true
        else false
    end as is_fab
from fancy_table

-- This rule can also simplify CASE statements
-- that aim to fill NULL values.

select
    case
        when fab is null then 0
        else fab
    end as fab_clean
from fancy_table

-- This also covers where the case statement
-- replaces NULL values with NULL values.

select
    case
        when fab is null then null
        else fab
    end as fab_clean
from fancy_table

Best practice

Reduce to WHEN condition within COALESCE function.

select
    coalesce(fab > 0, false) as is_fab
from fancy_table

-- To fill NULL values.

select
    coalesce(fab, 0) as fab_clean
from fancy_table

-- NULL filling NULL.

select fab as fab_clean
from fancy_table

Code ST03¶

Rule structure.unused_cte¶

Query defines a CTE (common-table expression) but does not use it.¶

Name: structure.unused_cte

Aliases: L045

Groups: all, core, structure

Anti-pattern

Defining a CTE that is not used by the query is harmless, but it means the code is unnecessary and could be removed.

WITH cte1 AS (
  SELECT a
  FROM t
),
cte2 AS (
  SELECT b
  FROM u
)

SELECT *
FROM cte1

Best practice

Remove unused CTEs.

WITH cte1 AS (
  SELECT a
  FROM t
)

SELECT *
FROM cte1

Code ST04¶

Rule structure.nested_case¶

Nested `CASE` statement in `ELSE` clause could be flattened.¶

This rule is sqlfluff fix compatible.

Name: structure.nested_case

Aliases: L058

Groups: all, structure

Anti-pattern

In this example, the outer CASE’s ELSE is an unnecessary, nested CASE.

SELECT
  CASE
    WHEN species = 'Cat' THEN 'Meow'
    ELSE
    CASE
       WHEN species = 'Dog' THEN 'Woof'
    END
  END as sound
FROM mytable

Best practice

Move the body of the inner CASE to the end of the outer one.

SELECT
  CASE
    WHEN species = 'Cat' THEN 'Meow'
    WHEN species = 'Dog' THEN 'Woof'
  END AS sound
FROM mytable

Code ST05¶

Rule structure.subquery¶

Join/From clauses should not contain subqueries. Use CTEs instead.¶

By default this rule is configured to allow subqueries within FROM clauses but not within JOIN clauses. If you prefer a stricter lint then this is configurable.

This rule is sqlfluff fix compatible.

Name: structure.subquery

Aliases: L042

Groups: all, structure

Configuration

forbid_subquery_in: Which clauses should be linted for subqueries? Must be one of ['join', 'from', 'both'].

Note

Some dialects don’t allow CTEs, and for those dialects this rule makes no sense and should be disabled.

Anti-pattern

select
    a.x, a.y, b.z
from a
join (
    select x, z from b
) using(x)

Best practice

with c as (
    select x, z from b
)
select
    a.x, a.y, c.z
from a
join c using(x)

Code ST06¶

Rule structure.column_order¶

Select wildcards then simple targets before calculations and aggregates.¶

This rule is sqlfluff fix compatible.

Name: structure.column_order

Aliases: L034

Groups: all, structure

Anti-pattern

select
    a,
    *,
    row_number() over (partition by id order by date) as y,
    b
from x

Best practice

Order select targets in ascending complexity

select
    *,
    a,
    b,
    row_number() over (partition by id order by date) as y
from x

Code ST07¶

Rule structure.using¶

Prefer specifying join keys instead of using `USING`.¶

This rule is sqlfluff fix compatible.

Name: structure.using

Aliases: L032

Groups: all, structure

Note

This rule was originally taken from the dbt Style Guide which notes that:

Certain warehouses have inconsistencies in USING results (specifically Snowflake).

In fact dbt removed it from their style guide in February 2022. However, some like the rule, so for now we will keep it in SQLFluff, but encourage those that do not find value in the rule, to turn it off.

Note

This rule is disabled for ClickHouse as it supports USING without brackets which this rule does not support.

Anti-pattern

SELECT
    table_a.field_1,
    table_b.field_2
FROM
    table_a
INNER JOIN table_b USING (id)

Best practice

Specify the keys directly

SELECT
    table_a.field_1,
    table_b.field_2
FROM
    table_a
INNER JOIN table_b
    ON table_a.id = table_b.id

Code ST08¶

Rule structure.distinct¶

`DISTINCT` used with parentheses.¶

This rule is sqlfluff fix compatible.

Name: structure.distinct

Aliases: L015

Groups: all, structure, core

Anti-pattern

In this example, parentheses are not needed and confuse DISTINCT with a function. The parentheses can also be misleading about which columns are affected by the DISTINCT (all the columns!).

SELECT DISTINCT(a), b FROM foo

Best practice

Remove parentheses to be clear that the DISTINCT applies to both columns.

SELECT DISTINCT a, b FROM foo

Code ST09¶

Rule structure.join_condition_order¶

Joins should list the table referenced earlier/later first.¶

This rule will break conditions from join clauses down into subconditions using the “and” and “or” binary operators.

Subconditions that are made up of a qualified column reference, a comparison operator and another qualified column reference are then evaluated to check whether they list the table that was referenced earlier - or later, depending on the preferred_first_table_in_join_clause configuration.

Subconditions that do not follow that pattern are ignored by this rule.

This rule is sqlfluff fix compatible.

Name: structure.join_condition_order

Groups: all, structure

Configuration

preferred_first_table_in_join_clause: Which table to list first when joining two tables. Defaults to earlier. Must be one of ['earlier', 'later'].

Note

Joins in WHERE clauses are currently not supported by this rule.

Anti-pattern

In this example, the tables that were referenced later are listed first and the preferred_first_table_in_join_clause configuration is set to earlier.

select
    foo.a,
    foo.b,
    bar.c
from foo
left join bar
    -- This subcondition does not list
    -- the table referenced earlier first:
    on bar.a = foo.a
    -- Neither does this subcondition:
    and bar.b = foo.b

Best practice

List the tables that were referenced earlier first.

select
    foo.a,
    foo.b,
    bar.c
from foo
left join bar
    on foo.a = bar.a
    and foo.b = bar.b

Code ST10¶

Rule structure.constant_expression¶

Redundant constant expression.¶

Including an expression that always evaluates to either TRUE or FALSE regardless of the input columns is unnecessary and makes statements harder to read and understand.

Constant conditions are sometimes mistakes (by mistyping the column name intended), and sometimes the result of incorrect information that they are necessary in some circumstances. In the former case, they can sometimes result in a cartesian join if it was supposed to be a join condition. Given the ambiguity of intent, this rule does not suggest an automatic fix, and instead invites the user to resolve the problem manually.

Name: structure.constant_expression

Groups: all, structure

Anti-pattern

SELECT *
FROM my_table
-- This following WHERE clause is redundant.
WHERE my_table.col = my_table.col

Best practice

SELECT *
FROM my_table
-- Replace with a condition that includes meaningful logic,
-- or remove the condition entirely.
WHERE my_table.col > 3

Code ST11¶

Rule structure.unused_join¶

Joined table not referenced in query.¶

This rule will check if there are any tables that are referenced in the FROM or JOIN clause of a SELECT statement, but where no columns from that table are referenced in the any of the other clauses. Because some types of join are often used as filters, or to otherwise control granularity without being referenced (e.g. INNER and CROSS), this rule only applies to explicit OUTER joins (i.e. LEFT, RIGHT and FULL joins).

This rule relies on all of the column references in the SELECT statement being qualified with at least the table name, and so is designed to work alongside references.qualification (RF02). This is because without the knowledge of what columns exist in each upstream table, the rule is unable to resolve which table an unqualified column reference is pulled from.

This rule does not propose a fix, because it assumes that it an unused table is a mistake, but doesn’t know whether the mistake was the join, or the mistake was not using it.

Name: structure.unused_join

Groups: all, structure

Anti-pattern

In this example, the table bar is included in the JOIN clause but not columns from it are referenced in

SELECT
    foo.a,
    foo.b
FROM foo
LEFT JOIN bar ON foo.a = bar.a

Best practice

Remove the join, or use the table.

SELECT foo.a, vee.b
FROM foo;

SELECT
    foo.a,
    foo.b,
    bar.c
FROM foo
LEFT JOIN bar ON foo.a = bar.a

In the (very rare) situations that it is logically necessary to include a table in a join clause, but not otherwise refer to it (likely for granularity reasons, or as a stepping stone to another table), we recommend ignoring this rule for that specific line by using -- noqa: ST10 at the end of the line.

TSQL bundle¶

Code TQ01¶

Rule tsql.sp_prefix¶

`SP_` prefix should not be used for user-defined stored procedures in T-SQL.¶

Name: tsql.sp_prefix

Aliases: L056

Groups: all, tsql

Anti-pattern

The SP_ prefix is used to identify system procedures and can adversely affect performance of the user-defined stored procedure. It can also break system procedures if there is a naming conflict.

 CREATE PROCEDURE dbo.sp_pull_data
 AS
 SELECT
     ID,
     DataDate,
     CaseOutput
 FROM table1

Best practice

Use a different name for the stored procedure.

 CREATE PROCEDURE dbo.pull_data
 AS
 SELECT
     ID,
     DataDate,
     CaseOutput
 FROM table1

 -- Alternatively prefix with USP_ to
 -- indicate a user-defined stored procedure.

 CREATE PROCEDURE dbo.usp_pull_data
 AS
 SELECT
     ID,
     DataDate,
     CaseOutput
 FROM table1

Rules Reference¶

Core Rules¶

Rule Index¶

Aliasing bundle¶

Implicit/explicit aliasing of table.¶

Implicit/explicit aliasing of columns.¶

Column expression without alias. Use explicit AS clause.¶

Table aliases should be unique within each clause.¶

Tables should not be aliased if that alias is not used.¶

Enforce table alias lengths in from clauses and join conditions.¶

Avoid table aliases in from clauses and join conditions.¶

Column aliases should be unique within each clause.¶

Column aliases should not alias to itself, i.e. self-alias.¶

Ambiguous bundle¶

Ambiguous use of DISTINCT in a SELECT statement with GROUP BY.¶

UNION [DISTINCT|ALL] is preferred over just UNION.¶

Ambiguous ordering directions for columns in order by clause.¶

Query produces an unknown number of result columns.¶

Join clauses should be fully qualified.¶

Inconsistent column references in GROUP BY/ORDER BY clauses.¶

Queries within set query produce different numbers of columns.¶

Implicit cross join detected.¶

Capitalisation bundle¶

Inconsistent capitalisation of keywords.¶

Inconsistent capitalisation of unquoted identifiers.¶

Inconsistent capitalisation of function names.¶

Inconsistent capitalisation of boolean/null literal.¶

Inconsistent capitalisation of datatypes.¶

Convention bundle¶

Consistent usage of != or <> for “not equal to” operator.¶

Use COALESCE instead of IFNULL or NVL.¶

Trailing commas within select clause.¶

Use consistent syntax to express “count number of rows”.¶

Comparisons with NULL should use “IS” or “IS NOT”.¶

Statements must end with a semi-colon.¶

Top-level statements should not be wrapped in brackets.¶

Use LEFT JOIN instead of RIGHT JOIN.¶

Block a list of configurable words from being used.¶

Consistent usage of preferred quotes for quoted literals.¶

Enforce consistent type casting style.¶

Use JOIN … ON … instead of WHERE … for join conditions.¶

Jinja bundle¶

Jinja tags should have a single whitespace on either side.¶

Layout bundle¶

Inappropriate Spacing.¶

Incorrect Indentation.¶

Operators should follow a standard for being before/after newlines.¶

Leading/Trailing comma enforcement.¶

Line is too long.¶

Function name not immediately followed by parenthesis.¶

WITH clause closing bracket should be on a new line.¶

Blank line expected but not found after CTE closing bracket.¶

Select targets should be on a new line unless there is only one select target.¶

SELECT modifiers (e.g. DISTINCT) must be on the same line as SELECT.¶

Set operators should be surrounded by newlines.¶

Files must end with a single trailing newline.¶

Files must not begin with newlines or whitespace.¶

Keyword clauses should follow a standard for being before/after newlines.¶

References bundle¶

References cannot reference objects not present in FROM clause.¶

References should be qualified if select has more than one referenced table/view.¶

Column references should be qualified consistently in single table statements.¶

Keywords should not be used as identifiers.¶

Do not use special characters in identifiers.¶

Unnecessary quoted identifier.¶

Structure bundle¶

Do not specify else null in a case when statement (redundant).¶

Unnecessary CASE statement.¶

Query defines a CTE (common-table expression) but does not use it.¶

Nested CASE statement in ELSE clause could be flattened.¶

Join/From clauses should not contain subqueries. Use CTEs instead.¶

Select wildcards then simple targets before calculations and aggregates.¶

Prefer specifying join keys instead of using USING.¶

DISTINCT used with parentheses.¶

Joins should list the table referenced earlier/later first.¶

Redundant constant expression.¶

Joined table not referenced in query.¶

TSQL bundle¶

SP_ prefix should not be used for user-defined stored procedures in T-SQL.¶

Ambiguous use of `DISTINCT` in a `SELECT` statement with `GROUP BY`.¶

`UNION [DISTINCT|ALL]` is preferred over just `UNION`.¶

Inconsistent column references in `GROUP BY/ORDER BY` clauses.¶

Consistent usage of `!=` or `<>` for “not equal to” operator.¶

Use `COALESCE` instead of `IFNULL` or `NVL`.¶

Use `LEFT JOIN` instead of `RIGHT JOIN`.¶

`WITH` clause closing bracket should be on a new line.¶

`SELECT` modifiers (e.g. `DISTINCT`) must be on the same line as `SELECT`.¶

References cannot reference objects not present in `FROM` clause.¶

Do not specify `else null` in a case when statement (redundant).¶

Unnecessary `CASE` statement.¶

Nested `CASE` statement in `ELSE` clause could be flattened.¶

Prefer specifying join keys instead of using `USING`.¶

`DISTINCT` used with parentheses.¶

`SP_` prefix should not be used for user-defined stored procedures in T-SQL.¶