MySQL WHERE

MySQL WHERE Clause: Filtering Query Results

The MySQL WHERE clause filters records so that only rows matching specified logical conditions are returned.

Supported Logical Operators in WHERE

• Comparison: =, !=, <>, >, <, >=, <=
• Range & Set: BETWEEN, IN, NOT IN
• Pattern Matching: LIKE, REGEXP
• NULL Checking: IS NULL, IS NOT NULL

Practical SQL Code Example

-- Query products priced greater than $50.00
SELECT product_name, price, category 
FROM products 
WHERE price > 50.00 AND status = 'ACTIVE';

Expected Output

Best Practices & Gotchas

• Use Index-Friendly Conditions: Avoid wrapping indexed columns in functions (e.g. WHERE YEAR(created_at) = 2026) because it prevents index usage. Use date ranges instead (WHERE created_at >= '2026-01-01').
• NULL Comparisons: Never use WHERE column = NULL. Always use WHERE column IS NULL.

Self-Check Challenge

What is the correct SQL syntax to check if a column value is missing or NULL?