Schema Design & Table Relationships

Normalization & Database Design Principles

Understanding NULL Values in SQL

Create a products table with appropriate data types and constraints

Add CHECK constraints to prevent negative prices and quantities

Design a users table with email validation

Compare storage sizes of different data types

What is the difference between CHAR and VARCHAR?

Why should you use DECIMAL instead of FLOAT for money?

Explain PRIMARY KEY vs UNIQUE constraint

What is a CHECK constraint and when would you use it?

When should you use NOT NULL vs allowing NULLs?

Why does implicit conversion kill performance? → Changes data type mid-query; indexed col becomes unseekable (scan). Demo: Execution plan shows "Convert(int)". Fix: Match types

Handle JSON in SQL without apps? → PostgreSQL: jsonb_array_elements(); SQL Server: OPENJSON(). Index GIN/JSON paths

Follow-ups: Overflow on CAST? (Yes, BIGINT→INT errors). TRY_CAST? (NULL safe)

SQL Data Types Reference

Database Constraints Guide

Choosing the Right Data Type

Financial Data Best Practices