SQL JOIN Quiz

What is the purpose of a JOIN in SQL?

• To delete rows from multiple tables

• To combine rows from two or more tables based on a related column

• To add new columns to a table

• To update data in a single table

Which of the following types of JOIN returns only matching rows from both tables?

• INNER JOIN

• LEFT JOIN

• RIGHT JOIN

• FULL OUTER JOIN

A LEFT JOIN will return rows from the left table with (a)   for non-matching rows in the right table.

• Only matching rows
• Rows from the left table with NULLs
• Only rows with NULL values
• An error

SELECT e.Name, d.DepartmentName

FROM Employees e

LEFT JOIN Departments d

ON e.DepartmentID = d.DepartmentID;

What is the result of the query?

• Alice - HR; Bob - NULL; Charlie - IT

• Alice - HR; Charlie - IT

• NULL - NULL

• Alice - HR; Bob - IT; Charlie - IT

Which JOIN should you use to include unmatched rows from both tables?

• INNER JOIN

• LEFT JOIN

• RIGHT JOIN

• FULL OUTER JOIN

What is the result of using an INNER JOIN with no matching records between tables?

• NULL rows

• No rows returned

• All rows from both tables

• Rows from the left table only

(a)   will produce the same result as reversing the roles of the two tables in a LEFT JOIN.

• INNER JOIN
• FULL OUTER JOIN
• RIGHT JOIN
• CROSS JOIN

Which JOIN returns all possible combinations of rows from two tables?

• INNER JOIN

• FULL OUTER JOIN

• RIGHT JOIN

• CROSS JOIN

What keyword is used to define the condition in a JOIN clause?

• WHERE

• USING

• ON

• JOIN

Consider the following query.

What does it do?

SELECT e.Name, p.ProjectName

FROM Employees e

INNER JOIN Projects p ON e.EmployeeID = p.ManagerID;

• Returns employees who are managing projects

• Returns all employees and their projects

• Returns projects without managers

• Returns all employees, whether they manage a project or not