Which of the following is the correct way to use EXISTS in a PostgreSQL query to check for related records?

easy📝 Syntax Q3 of 15

PostgreSQL - Subqueries in PostgreSQL

Which of the following is the correct way to use EXISTS in a PostgreSQL query to check for related records?

ASELECT * FROM employees WHERE EXISTS (SELECT 1 FROM tasks WHERE tasks.employee_id = employees.id);

BSELECT * FROM employees WHERE EXISTS SELECT 1 FROM tasks WHERE tasks.employee_id = employees.id;

CSELECT * FROM employees WHERE EXISTS (tasks.employee_id = employees.id);

DSELECT * FROM employees WHERE EXISTS (SELECT * FROM tasks WHERE tasks.employee_id = employees.id) = TRUE;

Step-by-Step Solution

Solution:

Step 1: Understand EXISTS syntax
EXISTS requires a subquery enclosed in parentheses that returns rows.
Step 2: Analyze options
SELECT * FROM employees WHERE EXISTS (SELECT 1 FROM tasks WHERE tasks.employee_id = employees.id); correctly uses EXISTS with a subquery in parentheses returning 1 for matching rows.
SELECT * FROM employees WHERE EXISTS SELECT 1 FROM tasks WHERE tasks.employee_id = employees.id; misses parentheses around the subquery.
SELECT * FROM employees WHERE EXISTS (tasks.employee_id = employees.id); uses an invalid condition inside EXISTS.
SELECT * FROM employees WHERE EXISTS (SELECT * FROM tasks WHERE tasks.employee_id = employees.id) = TRUE; compares EXISTS to TRUE, which is unnecessary and invalid syntax.
Final Answer:
Option A -> Option A
Quick Check:
EXISTS needs a subquery in parentheses [OK]

Quick Trick: EXISTS requires a subquery enclosed in parentheses [OK]

Common Mistakes:

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