[Solved] Given tables employees(id, name) and projects(id, employee_id), what does this query return?SELECT name FROM employees WHERE EXISTS (SELECT 1 FROM projects WHERE projects.employee_id = employees.id); | PostgreSQL

PostgreSQL - Subqueries in PostgreSQL

Given tables employees(id, name) and projects(id, employee_id), what does this query return?

SELECT name FROM employees WHERE EXISTS (SELECT 1 FROM projects WHERE projects.employee_id = employees.id);

AAn error because of missing JOIN

BNames of employees who have at least one project

CAll employee names regardless of projects

DNames of employees who have no projects

Step-by-Step Solution

Solution:

Step 1: Understand the EXISTS subquery
The subquery checks if any project exists for each employee by matching employee_id.
Step 2: Interpret the WHERE clause
WHERE EXISTS filters employees who have at least one matching project row.
Final Answer:
Names of employees who have at least one project -> Option B
Quick Check:
EXISTS filters employees with projects = D [OK]

Quick Trick: EXISTS filters rows where subquery finds matches [OK]

Common Mistakes:

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Given tables employees(id, name) and projects(id, employee_id), what does this query return?