**Performance Tips:**

- String functions in WHERE prevent index usage

- Use functional indexes for UPPER/LOWER searches

- Normalize data at insert time when possible

- LIKE with leading % cannot use index

- Store lowercase/uppercase versions for fast searches

Functions in WHERE = Full Table Scan

LIKE with Leading %: Cannot use index

Use Functional Indexes: CREATE INDEX ON users(LOWER(email))

Normalize Early: Pre-store LOWER(email), TRIM(name)

NULL Concatenation: 'John' || NULL || 'Doe' → NULL

String Functions in WHERE Prevent Indexes

Cross-DB Concatenation Differences: || fails in MySQL

LIKE Case Sensitivity Varies by database