SQL Syntax Checker

Validate SQL syntax, identify errors, and ensure queries are structurally correct before execution.

Trigger Conditions

Activate this skill when the user:

•Says "check this SQL", "validate my query", "is this correct"
•Pastes SQL and asks if it will work
•Gets a syntax error and needs help understanding it
•Wants to verify SQL before running on production
•Asks about SQL syntax rules

Validation Workflow

code

1. PARSE       -> Analyze query structure
2. IDENTIFY    -> Detect the SQL dialect
3. CHECK       -> Validate against syntax rules
4. REPORT      -> List errors with line numbers
5. FIX         -> Provide corrected version

Pre-Flight Checklist

Before validating any query:

code

- [ ] Identified target database dialect
- [ ] Checked for complete query (no truncation)
- [ ] Noted any placeholders or parameters

Common Syntax Rules

Universal Rules (All Dialects)

Rule	Correct	Incorrect
Keywords	Case-insensitive	N/A
Identifiers	Letters, numbers, underscores	Starting with numbers
String literals	Single quotes	Double quotes (most dialects)
Statement terminator	Semicolon	None (depends on context)
Comments	-- or /* */	# (MySQL only)

SELECT Statement Structure

sql

SELECT [DISTINCT | ALL]
    column_list
FROM table_reference
    [JOIN clause]
[WHERE condition]
[GROUP BY expression_list]
[HAVING condition]
[ORDER BY expression_list [ASC | DESC]]
[LIMIT count [OFFSET start]]

Common errors:

•Columns in SELECT not in GROUP BY (when not aggregated)
•ORDER BY position number exceeding column count
•HAVING without GROUP BY
•Missing table alias with ambiguous column names

Clause Order Validation

code

Required order:
1. SELECT
2. FROM
3. WHERE
4. GROUP BY
5. HAVING
6. ORDER BY
7. LIMIT/OFFSET

Syntax Error Patterns

Missing or Mismatched Parentheses

Error:

sql

SELECT * FROM users WHERE (status = 'active' AND (role = 'admin')

Fixed:

sql

SELECT * FROM users WHERE (status = 'active' AND role = 'admin')

Incorrect String Quotes

Error (most dialects):

sql

SELECT * FROM users WHERE name = "John"

Fixed:

sql

SELECT * FROM users WHERE name = 'John'

Missing Commas in Column List

Error:

sql

SELECT id name email FROM users

Fixed:

sql

SELECT id, name, email FROM users

Invalid Column Reference in ORDER BY

Error:

sql

SELECT name, COUNT(*) FROM users GROUP BY name ORDER BY email

Fixed:

sql

SELECT name, COUNT(*) FROM users GROUP BY name ORDER BY name

Missing JOIN Condition

Error:

sql

SELECT * FROM orders o JOIN customers c

Fixed:

sql

SELECT * FROM orders o JOIN customers c ON o.customer_id = c.id

Aggregate Without GROUP BY

Error:

sql

SELECT department, name, COUNT(*) FROM employees

Fixed:

sql

SELECT department, COUNT(*) FROM employees GROUP BY department

Invalid NULL Comparison

Error:

sql

SELECT * FROM users WHERE deleted_at = NULL

Fixed:

sql

SELECT * FROM users WHERE deleted_at IS NULL

Ambiguous Column Reference

Error:

sql

SELECT id, name FROM users u JOIN orders o ON u.id = o.user_id

Fixed:

sql

SELECT u.id, u.name FROM users u JOIN orders o ON u.id = o.user_id

Dialect-Specific Validation

PostgreSQL Specifics

Feature	PostgreSQL Syntax
String concat	`'a'
Case sensitivity	Identifiers lowercase unless quoted
Boolean	`TRUE`, `FALSE`, `'t'`, `'f'`
Array access	`array_col[1]` (1-indexed)
JSON access	`json_col->>'key'` or `json_col->'key'`
Type cast	`value::type` or `CAST(value AS type)`

MySQL Specifics

Feature	MySQL Syntax
String concat	`CONCAT('a', 'b')`
Identifier quotes	Backticks: `table_name`
Limit with offset	`LIMIT offset, count` or `LIMIT count OFFSET offset`
Auto increment	`AUTO_INCREMENT`
Boolean	`1`, `0`, `TRUE`, `FALSE`

SQL Server Specifics

Feature	SQL Server Syntax
String concat	`'a' + 'b'` or `CONCAT('a', 'b')`
Identifier quotes	Square brackets: `[table_name]`
Top N rows	`SELECT TOP 10 *`
Identity	`IDENTITY(1,1)`
Date functions	`GETDATE()`, `DATEADD()`, `DATEDIFF()`

Oracle Specifics

Feature	Oracle Syntax
String concat	`'a'
Row limiting	`FETCH FIRST 10 ROWS ONLY` (12c+)
Sequence	`sequence_name.NEXTVAL`
From dual	Required for SELECT without table
NVL	Use `NVL(col, default)` for null handling

SQLite Specifics

Feature	SQLite Syntax
Auto increment	`INTEGER PRIMARY KEY` (automatic)
Boolean	`0` and `1` (no boolean type)
Type affinity	Flexible typing
Limit	`LIMIT count OFFSET start`
Date functions	`date()`, `datetime()`, `strftime()`

Validation Checklist

Structure Validation

code

- [ ] All keywords spelled correctly
- [ ] Clauses in correct order
- [ ] Required clauses present (SELECT, FROM for queries)
- [ ] Parentheses balanced and matched
- [ ] All expressions complete

Reference Validation

code

- [ ] All column names valid or aliased
- [ ] All table names valid or aliased
- [ ] Aliases used consistently
- [ ] No ambiguous references
- [ ] Subquery columns accessible

Type Validation

code

- [ ] Comparison types compatible
- [ ] Function arguments correct type
- [ ] Literals properly quoted
- [ ] Date/time formats valid
- [ ] Numeric precision appropriate

Logic Validation

code

- [ ] JOINs have ON conditions
- [ ] WHERE conditions make sense
- [ ] GROUP BY includes all non-aggregated columns
- [ ] HAVING uses aggregate functions
- [ ] No circular references

Error Message Interpretation

PostgreSQL Errors

Error	Meaning	Solution
`syntax error at or near "X"`	Unexpected token	Check syntax before token X
`column "X" does not exist`	Unknown column	Verify column name/alias
`relation "X" does not exist`	Unknown table	Verify table name
`column "X" must appear in GROUP BY`	Missing grouping	Add column to GROUP BY or aggregate
`operator does not exist: X`	Type mismatch	Cast types appropriately

MySQL Errors

Error	Meaning	Solution
`You have an error in your SQL syntax`	Parse error	Check near indicated position
`Unknown column 'X'`	Column not found	Verify column/alias
`Table 'X' doesn't exist`	Table not found	Verify table name
`Mixing of GROUP columns`	Invalid grouping	Fix GROUP BY
`Duplicate entry 'X' for key`	Unique violation	Handle duplicates

SQL Server Errors

Error	Meaning	Solution
`Incorrect syntax near 'X'`	Parse error	Check syntax
`Invalid column name 'X'`	Unknown column	Verify column
`Invalid object name 'X'`	Unknown table	Verify table
`Column 'X' is invalid in the select list`	Missing GROUP BY	Fix grouping
`Conversion failed`	Type error	Cast appropriately

Output Format

When validating SQL, provide:

•Status: Valid or Invalid
•Errors Found: List with line numbers
•Warnings: Non-critical issues
•Corrected Query: If errors found
•Explanation: What was wrong and why

Example output:

code

Status: INVALID

Errors Found:
1. Line 3: Missing comma between columns
2. Line 5: Unclosed parenthesis
3. Line 7: Unknown column 'user_name' - did you mean 'username'?

Warnings:
1. SELECT * is discouraged - specify columns explicitly
2. Missing table alias may cause ambiguity with JOINs

Corrected Query:
[corrected SQL here]

Explanation:
[detailed explanation]

Additional Resources

File	Content
examples.md	Common syntax errors and corrections