Code Quality

Querylab.io analyzes your SQL in real-time and highlights issues with colored underlines.

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Severity Levels

Color	Severity	Meaning
Red	Error	Query will fail — must fix
Orange	Warning	Cost/performance issue — should fix
Blue	Info	Potential improvement
Dotted	Hint	Optional optimization

Hover over any underline to see details. Press Cmd+. (Mac) or Ctrl+. (Windows) for quick fixes.

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Rules

Cost & Performance

• SELECT * on large table
• Large table scan without filters
• Missing partition filter
• Missing cluster filter

• Wildcard table scan without filter
• Wildcard table scan without _TABLE_SUFFIX
• ORDER BY without LIMIT
• COUNT(DISTINCT) performance
• Suboptimal clustering order

JOIN Issues

• CROSS JOIN detected
• JOIN with OR condition
• Missing JOIN condition
• Ambiguous SELECT * with JOINs

NULL Handling

• NULL comparison with =

Column References

• Undefined column
• Column references without FROM clause
• Ambiguous column reference
• Duplicate column/alias
• Conflicting column and alias names
• USING clause references non-existent column

GROUP BY & Aggregation

• Non-aggregated column in GROUP BY
• HAVING without GROUP BY
• Aggregate in WHERE clause
• Nested aggregate functions
• SELECT * with GROUP BY

Window Functions

• Window function in WHERE
• QUALIFY without window function

CTEs

• Unused CTE
• Duplicate CTE name
• Undefined CTE references
• CTE shadows table (disabled)

ORDER BY

• ORDER BY column not in SELECT
• ORDER BY position out of range
• LIMIT without ORDER BY in subquery

Type Consistency

• String in numeric comparison
• CASE expression with inconsistent types

Subqueries

• Unnecessary subquery wrapping
• Scalar subquery returning multiple columns
• IN subquery returning multiple columns

Table & Alias References

• Undefined table alias
• Duplicate table aliases
• Invalid hierarchical naming (project.dataset.table)

Suggestions (lightbulb only)

• Suggest using QUALIFY clause — detects the old subquery + WHERE rn = 1 pattern and suggests the modern QUALIFY syntax
• Suggest GROUP BY ALL
• Suggest UNION BY NAME
• Suggest LIKE ANY — detects col LIKE '%A' OR col LIKE '%B' and suggests col LIKE ANY ('%A', '%B')

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Example: QUALIFY Suggestion

Querylab.io detects when you use the common subquery workaround for ranking and suggests the cleaner QUALIFY syntax.

Before (subquery workaround):

SELECT * FROM (
  SELECT
    user_id,
    status,
    ROW_NUMBER() OVER(PARTITION BY user_id ORDER BY timestamp DESC) AS rn
  FROM `my-project.dataset.table`
)
WHERE rn = 1

After (QUALIFY):

SELECT
  user_id,
  status
FROM `my-project.dataset.table`
QUALIFY ROW_NUMBER() OVER(PARTITION BY user_id ORDER BY timestamp DESC) = 1

After (Pipe syntax):

FROM `my-project.dataset.table`
|> QUALIFY ROW_NUMBER() OVER(PARTITION BY user_id ORDER BY timestamp DESC) = 1
|> SELECT user_id, status

Works with ROW_NUMBER(), RANK(), and DENSE_RANK().

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Example: LIKE ANY Suggestion

Querylab.io detects when you use multiple OR conditions with LIKE on the same column and suggests the more concise LIKE ANY syntax.

Before (multiple OR conditions):

SELECT * FROM users
WHERE name LIKE '%smith' OR name LIKE '%jones' OR name LIKE '%doe'

After (LIKE ANY):

SELECT * FROM users
WHERE name LIKE ANY ('%smith', '%jones', '%doe')

Also works with NOT LIKE conditions, suggesting NOT LIKE ANY.

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Configuring Rules

Settings → Diagnostic Rules to enable/disable specific rules.