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Correlated subquery
Learn Correlated subquery in Oracle SQL through the exact construct, a dedicated example, a boundary case, and a mastery check.
Correlated subquery is an atomic Oracle SQL lesson inside Queries & Joins. The example uses the specific syntax, command, API, instruction, or language rule named by this lesson.
Study the construct itself, then change one relevant input and predict the result before running it. That keeps this lesson focused on Correlated subquery rather than on generic Oracle SQL syntax.
Topic-specific example
SELECT e.employee_id,(SELECT COUNT(*) FROM tasks t WHERE t.owner_id=e.employee_id) task_count FROM employees e;
Test Correlated subquery with an empty result, NULL/missing value, duplicate key, or concurrent operation where relevant; database behavior should be verified at the boundary shown by this example.