**Performance Tips:**

- Calculations in SELECT are cheap (computed per returned row)

- Calculations in WHERE can prevent index usage

- Use computed columns for frequently calculated values

- Aggregate functions require full table scan unless indexed

- Functions on indexed columns break indexes

- DECIMAL math is slower than FLOAT but required for financial precision

Calculations in SELECT are cheap

Avoid calculations in WHERE (breaks indexes)

Use computed columns for repeated calculations

Functions on columns in WHERE: 100x slower

Integer division truncates decimals

NULL in calculations returns NULL

Overflow in large calculations

Using FLOAT for money (rounding errors)

Math functions in WHERE break indexes