[Solved] Consider these tables:departmentsid | name1 | HR2 | IT3 | Salesemployeesid | dept_id | name1 | 2 | Alice2 | 2 | Bob3 | 4 | CarolWhat will this query return?SELECT departments.name, employees.... | PostgreSQL

PostgreSQL - Joins in PostgreSQL

Consider these tables:

departments
id | name
1 | HR
2 | IT
3 | Sales

employees
id | dept_id | name
1 | 2 | Alice
2 | 2 | Bob
3 | 4 | Carol

What will this query return?

SELECT departments.name, employees.name FROM departments RIGHT JOIN employees ON departments.id = employees.dept_id ORDER BY employees.id;

A[{"name": "IT", "name": "Alice"}, {"name": "IT", "name": "Bob"}]

B[{"name": "HR", "name": "Alice"}, {"name": "IT", "name": "Bob"}, {"name": "Sales", "name": "Carol"}]

C[{"name": "HR", "name": "Alice"}, {"name": "IT", "name": "Bob"}]

D[{"name": "IT", "name": "Alice"}, {"name": "IT", "name": "Bob"}, {"name": null, "name": "Carol"}]

Step-by-Step Solution

Solution:

Step 1: Understand RIGHT JOIN with departments and employees
RIGHT JOIN keeps all employees (right table). For each employee, it tries to find matching department by dept_id.
Step 2: Match employees to departments
Alice and Bob have dept_id=2 (IT). Carol has dept_id=4 which does not exist in departments, so department name is NULL.
Final Answer:
All employees appear with their department name or NULL if no match. -> Option D
Quick Check:
RIGHT JOIN keeps all right rows; unmatched left columns are NULL [OK]

Quick Trick: RIGHT JOIN keeps all right table rows; unmatched left columns NULL [OK]

Common Mistakes:

Assuming unmatched right rows are dropped
Mixing up which table is left or right
Expecting INNER JOIN behavior

Master "Joins in PostgreSQL" in PostgreSQL

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Consider these tables:

Step 1: Understand RIGHT JOIN with departments and employees

Step 2: Match employees to departments

Final Answer:

Quick Check:

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