/analyze-query

Analyze Query

Systematically analyze a T-SQL query for optimization opportunities.

Process

Step 1: Get Query

If user provided a file path:

# Read the query from file
cat "$1"

If user pasted query directly, use that.

Step 2: SARGability Analysis

Check for non-SARGable patterns:

Pattern	Issue	Fix
YEAR(DateCol) = 2024	Function on column	DateCol >= '2024-01-01' AND DateCol < '2025-01-01'
LEFT(Col, 3) = 'ABC'	Function on column	Col LIKE 'ABC%'
Col * 1.1 > 100	Arithmetic on column	Col > 100 / 1.1
ISNULL(Col, 0) = 5	Function on column	(Col = 5 OR Col IS NULL)
@Var = Col	Variable on left	Col = @Var

Step 3: Implicit Conversion Check

Look for potential type mismatches:

• VARCHAR column compared to INT value
• NVARCHAR vs VARCHAR comparisons
• Date strings without explicit CAST/CONVERT

Step 4: Join Analysis

For each JOIN:

• Check if join columns should be indexed
• Identify potential Cartesian products
• Look for inefficient OR conditions across tables

Step 5: Subquery Analysis

Check for:

• Correlated subqueries that could be JOINs
• IN vs EXISTS optimization opportunities
• Subqueries in SELECT that could use APPLY

Step 6: Index Recommendations

Based on:

• WHERE clause columns (equality first, then inequality)
• JOIN columns
• ORDER BY columns
• SELECT columns (for covering index)

Suggest CREATE INDEX statement.

Step 7: Generate Report

================================
Query Analysis Report
================================

QUERY:
[First 200 chars of query...]

SARGABILITY ISSUES:
[ ] WHERE YEAR(OrderDate) = 2024
    → Change to: WHERE OrderDate >= '2024-01-01' AND OrderDate < '2025-01-01'

IMPLICIT CONVERSIONS:
[ ] Line 5: VarcharColumn = 123
    → Change to: VarcharColumn = '123'

JOIN OPTIMIZATION:
[✓] CustomerID join column should have index
[ ] Consider EXISTS instead of IN for large subquery

INDEX RECOMMENDATIONS:
CREATE NONCLUSTERED INDEX IX_Orders_CustomerDate
ON Orders(CustomerID, OrderDate)
INCLUDE (Amount, Status);

ESTIMATED IMPACT: High
================================

Usage

# Analyze pasted query
/analyze-query SELECT * FROM Orders WHERE YEAR(OrderDate) = 2024

# Analyze query from file
/analyze-query queries/slow_report.sql

Tips

• For complex queries, break into CTEs for analysis
• Consider execution plan for actual performance data
• Test changes in non-production first
• Update statistics after adding indexes