beginner~3h
SQL Fundamentals Deep Dive — Data Types, NULL Handling & Query Execution Order
The data type you pick, how you handle NULL, and the order SQL actually evaluates a query's clauses in are three foundational things that quietly cause a disproportionate share of real-world SQL bugs.
Learning objectives
- Explain why NULL = NULL evaluates to unknown rather than true, and what that means for WHERE clauses.
- Choose the correct data type for money, text, and timestamps, and explain why the wrong choice causes real bugs, not just style complaints.
- State SQL's logical clause execution order and use it to predict which aliases are visible in which clauses.
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SQL Fundamentals Deep Dive — Data Types, NULL Handling & Query Execution Order