You want to list all departments and their employees, including departments with no employees. Which query achieves this?

hard📝 Application Q15 of 15

PostgreSQL - Joins in PostgreSQL

ASELECT departments.dept_name, employees.name FROM employees RIGHT JOIN departments WHERE employees.id = departments.id;

BSELECT departments.dept_name, employees.name FROM employees LEFT JOIN departments ON employees.id = departments.id;

CSELECT departments.dept_name, employees.name FROM departments RIGHT JOIN employees ON departments.id = employees.id;

DSELECT departments.dept_name, employees.name FROM departments LEFT JOIN employees ON departments.id = employees.id;

Step-by-Step Solution

Solution:

Step 1: Identify which table to keep all rows from
We want all departments, even those without employees, so departments is the left table in LEFT JOIN.
Step 2: Use LEFT JOIN from departments to employees
LEFT JOIN keeps all departments and adds matching employees or NULL if none.
Final Answer:
SELECT departments.dept_name, employees.name FROM departments LEFT JOIN employees ON departments.id = employees.id; -> Option D
Quick Check:
LEFT JOIN from departments keeps all departments [OK]

Quick Trick: LEFT JOIN from main table keeps all its rows, unmatched get NULLs [OK]

Common Mistakes:

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