[Solved] Why do we use subqueries in PostgreSQL?SELECT * FROM employees WHERE department_id IN (SELECT id FROM departments WHERE location = 'NY'); | PostgreSQL

PostgreSQL - Subqueries in PostgreSQL

Why do we use subqueries in PostgreSQL?
SELECT * FROM employees WHERE department_id IN (SELECT id FROM departments WHERE location = 'NY');

ATo change data types of columns

BTo speed up the database server automatically

CTo ask a question inside another query and filter results based on it

DTo create new tables from existing ones

Step-by-Step Solution

Solution:

Step 1: Understand the role of the subquery
The subquery (SELECT id FROM departments WHERE location = 'NY') finds department IDs located in NY.
Step 2: See how the main query uses the subquery
The main query selects employees whose department_id matches any ID from the subquery result.
Final Answer:
To ask a question inside another query and filter results based on it -> Option C
Quick Check:
Subqueries filter data using inner query results [OK]

Quick Trick: Subqueries answer inner questions to filter outer query [OK]

Common Mistakes:

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Why do we use subqueries in PostgreSQL?