Data Types & Constraints

WHERE Clause & Filtering

COUNT, SUM, AVG, MIN, MAX

Find rows with NULL values

Use COALESCE for fallback values

Handle NULL in calculations

Compare COUNT(*) vs COUNT(column)

What is NULL and how is it different from empty string?

Explain three-valued logic

How do aggregates handle NULL?

What is COALESCE and when to use it?

NULL Handling Guide

Three-Valued Logic Explained

COALESCE Function