[Solved] Which of the following is a correct syntax for using a subquery in the WHERE clause? — Ans: SELECT * FROM employees WHERE department_id = (SELECT id FROM departments WHERE... | SQL

SQL - Subqueries

Which of the following is a correct syntax for using a subquery in the WHERE clause?

ASELECT * FROM employees WHERE SELECT id FROM departments WHERE name = 'Sales' = department_id;

BSELECT * FROM employees WHERE department_id == (SELECT id FROM departments WHERE name = 'Sales');

CSELECT * FROM employees WHERE department_id IN SELECT id FROM departments WHERE name = 'Sales';

DSELECT * FROM employees WHERE department_id = (SELECT id FROM departments WHERE name = 'Sales');

Step-by-Step Solution

Solution:

Step 1: Check correct subquery syntax in WHERE clause
SELECT * FROM employees WHERE department_id = (SELECT id FROM departments WHERE name = 'Sales'); uses correct syntax: column = (subquery) with parentheses around the subquery.
Step 2: Identify errors in other options
SELECT * FROM employees WHERE SELECT id FROM departments WHERE name = 'Sales' = department_id; misses parentheses around subquery. SELECT * FROM employees WHERE department_id IN SELECT id FROM departments WHERE name = 'Sales'; misses parentheses around subquery. SELECT * FROM employees WHERE department_id == (SELECT id FROM departments WHERE name = 'Sales'); uses '==' which is not valid SQL syntax.
Final Answer:
SELECT * FROM employees WHERE department_id = (SELECT id FROM departments WHERE name = 'Sales'); -> Option D
Quick Check:
Correct subquery syntax = SELECT * FROM employees WHERE department_id = (SELECT id FROM departments WHERE name = 'Sales'); [OK]

Quick Trick: Always enclose subquery in parentheses in WHERE clause [OK]

Common Mistakes:

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Which of the following is a correct syntax for using a subquery in the WHERE clause?