A subquery expresses a query inside another query. A regular view stores a query definition rather than automatically creating a frozen copy of its results.
Before you begin
Use a disposable practice database with fictional tables. Record the database dialect and schema; syntax and features can differ between systems.
Work through the idea
Write down what one row represents and which keys should be unique. Predict a small result by hand before running a query. Compare row counts and totals after filtering or joining. Keep null handling, duplicate keys and date boundaries explicit so that a plausible output does not hide an incorrect query.
- Identify the inner query's output
- Compare a join and subquery
- Document the view's filter rules
Practice task
Define a view for fictional active customers and query their order totals.
Check your result
Explain how underlying record changes affect the view's result.
A mistake to avoid
Do not assume a regular view has independent stored data or built-in ordering.
Keep a review note
Save the inputs or scenario, your reasoning and the result you checked. Explain one assumption and one case that needs more work. Revise the exercise after feedback and distinguish what you demonstrated from what remains untested.
Official reference for further study
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