SQL Linter & Style Checker

A formatter fixes how SQL looks; a linter tells you what is wrong with it. This checker reads your statement and flags the problems that reviewers actually catch — an UPDATE with no WHERE clause, a NOT IN subquery that silently returns nothing when it hits a NULL, a function wrapped around an indexed column, a comma join whose predicate went missing, LIMIT with no ORDER BY — alongside style rules for keyword casing, line length and comma placement. Every rule runs in your browser, so nothing you paste leaves the page.

DialectKeyword caseMax line length

SQL

Lint report

21 issues — 2 error, 6 warning, 13 info
---------------------------------------

line 1  [WARNING]  S002 select-star
    SELECT * returns every column, including ones added later.
    Fix: List the columns you actually read so the result set stays stable and the planner can use covering indexes.

line 1  [WARNING]  S009 implicit-join
    Tables are joined with a comma in the FROM clause (implicit join).
    Fix: Use explicit JOIN ... ON syntax so the join condition cannot be lost in a long WHERE clause.

line 1  [INFO]  L006 keyword-case
    Keyword "select" is not uppercase.
    Fix: Write reserved words in UPPERCASE consistently across the file.

line 2  [INFO]  L006 keyword-case
    Keyword "where" is not uppercase.
    Fix: Write reserved words in UPPERCASE consistently across the file.

line 3  [INFO]  L006 keyword-case
    Keyword "and" is not uppercase.
    Fix: Write reserved words in UPPERCASE consistently across the file.

line 4  [WARNING]  P001 non-sargable-function
    A function is applied to a column inside a predicate, which prevents a plain index on that column from being used.
    Fix: Rewrite as a range predicate (col >= x AND col < y) or add a matching expression index.

line 4  [INFO]  L006 keyword-case
    Keyword "and" is not uppercase.
    Fix: Write reserved words in UPPERCASE consistently across the file.

line 5  [WARNING]  P002 leading-wildcard
    LIKE pattern starts with a wildcard, so a b-tree index cannot be used.
    Fix: Anchor the pattern, or use a trigram index (pg_trgm) / full text search for infix matching.

line 5  [INFO]  L006 keyword-case
    Keyword "and" is not uppercase.
    Fix: Write reserved words in UPPERCASE consistently across the file.

line 6  [ERROR]  S004 not-in-subquery
    NOT IN with a subquery returns zero rows if the subquery yields a single NULL.
    Fix: Use NOT EXISTS, or add a WHERE ... IS NOT NULL guard inside the subquery.

line 6  [INFO]  L006 keyword-case
    Keyword "and" is not uppercase.
    Fix: Write reserved words in UPPERCASE consistently across the file.

line 7  [WARNING]  S003 order-by-ordinal
    ORDER BY uses a column position instead of a name.
    Fix: Order by the expression or an alias; ordinals silently break when the SELECT list is reordered.

line 7  [INFO]  L006 keyword-case
    Keyword "order" is not uppercase.
    Fix: Write reserved words in UPPERCASE consistently across the file.

line 8  [INFO]  L006 keyword-case
    Keyword "limit" is not uppercase.
    Fix: Write reserved words in UPPERCASE consistently across the file.

line 9  [INFO]  L005 missing-semicolon
    Statement is not terminated with a semicolon.
    Fix: Terminate every statement; scripts run through psql or a migration tool need it to split batches.

line 10  [ERROR]  S007 update-without-where
    UPDATE has no WHERE clause and will rewrite every row in the table.
    Fix: Add a WHERE clause, or wrap the statement in an explicit transaction you can roll back.

line 10  [INFO]  L006 keyword-case
    Keyword "update" is not uppercase.
    Fix: Write reserved words in UPPERCASE consistently across the file.

line 11  [INFO]  L005 missing-semicolon
    Statement is not terminated with a semicolon.
    Fix: Terminate every statement; scripts run through psql or a migration tool need it to split batches.

line 12  [WARNING]  D001 no-primary-key
    CREATE TABLE declares no PRIMARY KEY.
    Fix: Give every table a primary key; replication, upserts and most ORMs depend on one.

line 12  [INFO]  L006 keyword-case
    Keyword "create" is not uppercase.
    Fix: Write reserved words in UPPERCASE consistently across the file.

line 16  [INFO]  L005 missing-semicolon
    Statement is not terminated with a semicolon.
    Fix: Terminate every statement; scripts run through psql or a migration tool need it to split batches.

Do more than sql linter & style checker — meet Chat2DB

Chat2DB is an AI-powered SQL client for Windows, macOS and Linux. Write SQL in natural language, format and optimize queries automatically, and manage MySQL, PostgreSQL, Oracle and 20+ other databases in one workspace.

How to use

Paste one or more SQL statements into the editor; the linter re-runs on every keystroke.
Choose your dialect, the keyword case your team uses and a maximum line length so the style rules match your conventions.
Work through the report from errors to info, using the fix hint on each finding, then re-check until the statement is clean.

Frequently asked questions

What is the difference between a SQL linter and a SQL formatter?

A formatter only changes whitespace and casing: it rewrites your query into a canonical layout without altering what the query does. A linter reads the query and reports problems — correctness traps such as an UPDATE with no WHERE clause or a NOT IN subquery that returns nothing when it encounters a NULL, performance traps such as a function applied to an indexed column, and style deviations such as inconsistent keyword casing. In practice teams run both: the formatter normalises the text and the linter gates the pull request. Tools like SQLFluff bundle the two; this page focuses on the linting half and runs entirely client-side.

Which SQL problems does this linter detect?

Correctness: comparing to NULL with = or <>, NOT IN against a subquery that can produce NULL, UPDATE or DELETE without a WHERE clause, a JOIN with no ON or USING clause, and COUNT(DISTINCT *). Performance: a leading wildcard in a LIKE pattern, functions applied to columns inside predicates, LIMIT without ORDER BY, and SELECT * in the projection. Schema: a CREATE TABLE with no primary key and, on dialects that require it, VARCHAR declared without a length. Style: keyword casing, tab indentation, trailing whitespace, over-long lines, leading commas, ordinal ORDER BY, mixed != and <> and missing statement terminators.

Is my SQL sent to a server?

No. The rules are plain JavaScript that runs in your browser tab, so the statement never leaves your machine and nothing is stored or logged. That makes it safe to paste production queries that contain table names or literal values you would not want to upload. If you want the same checks against a live connection — running EXPLAIN on the query the linter flagged, or browsing the schema behind it — Chat2DB is an AI SQL client for PostgreSQL, MySQL, Oracle and 20+ other engines; download it at https://chat2db.ai/download or open https://app.chat2db.ai in a browser.