Why this lesson matters

Understand where filtering and reason about it with a concrete relational example. SELECT should retrieve only the columns and rows the caller needs, with deterministic ordering when pagination or “latest” semantics matter.

How to reason about it

  • For WHERE Filtering, the outcome to verify is: Run the statement against sample data and inspect the result before moving to the next case.
  • In WHERE Filtering, keep this failure controlled: SELECT * on large tables and unbounded queries increase network, memory and privacy exposure while making application contracts less explicit.
  • WHERE Filtering practice target: Write a query that selects two columns, filters active rows, sorts newest first and limits the result.

Practical walkthrough

In the WHERE Filtering walkthrough: Run the statement against sample data and inspect the result before moving to the next case.

example.sqlsql
SELECT id, name
FROM customers
WHERE status = 'ACTIVE';

Practice it yourself

Practice

WHERE Filtering exercise

Write a query that selects two columns, filters active rows, sorts newest first and limits the result.

  • Record the expected result before execution
  • Test one valid path and one lesson-specific failure path
  • Explain in two lines which boundary owns the decision

Summary