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Oracle SQL Complete Course / Queries & Joins

Correlated subquery

Learn Correlated subquery in Oracle SQL through the exact construct, a dedicated example, a boundary case, and a mastery check.

10 min read • Beginner

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

oraclesql-02-08.sql
sql Try It Live
SELECT e.employee_id,(SELECT COUNT(*) FROM tasks t WHERE t.owner_id=e.employee_id) task_count FROM employees e;
Edge case / engineering note

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.

Content source & attribution
Original Syntaxis Content · Original Syntaxis Content