MySQL Joins Quiz – Answertopia

Joins allow us to combine data from multiple tables based on a common column, helping retrieve meaningful results efficiently. MySQL supports INNER JOIN, LEFT JOIN, RIGHT JOIN, CROSS JOIN, and FULL OUTER JOIN(simulated using UNION).

The UNION and UNION ALL operators merge result sets from multiple queries, with UNION removing duplicates and UNION ALL keeping them.

This quiz will test your understanding of MySQL joins and unions.

What happens if you perform a RIGHT JOIN and there are no matching records in the left table?

The query fails

Only matching rows are shown

No rows are returned

The rows from the right table are displayed with NULL values for the left table columns

None

What is the purpose of the ON clause in a JOIN statement?

To combine duplicate records

To remove NULL values

To sort query results

To specify the condition for joining tables

None

What does a CROSS JOIN do?

None of the above

Returns all possible combinations of rows from two tables

Matches rows from both tables based on a common column

Joins two tables and excludes NULL values

None

What is the difference between UNION and UNION ALL?

UNION ALL removes duplicate rows, while UNION includes them

UNION only works with INNER JOIN

UNION removes duplicate rows, while UNION ALL includes them

There is no difference

None

What will a LEFT JOIN return if there are no matching records in the right table?

All rows from the left table with NULL values for non-matching rows

All rows from the right table

No results

Only matching rows

None

What does the USING clause do in a JOIN?

Combines multiple columns into a single key

Specifies a common column between two tables without prefixing table names

Removes duplicate rows

Creates a new index on the table

None

What is the primary purpose of using joins in MySQL?

To combine rows from two or more tables based on related columns

To delete duplicate records

To create new tables

To improve indexing performance

None

Which statement correctly performs an INNER JOIN between two tables named 'customers' and 'orders'?

SELECT * FROM customers, orders;

SELECT * FROM customers CROSS JOIN orders;

SELECT * FROM customers INNER JOIN orders ON customers.id = orders.customer_id;

SELECT * FROM customers JOIN orders;

None

Which type of join can result in a Cartesian product?

RIGHT JOIN

CROSS JOIN

INNER JOIN

LEFT JOIN

None

10.

Which MySQL function is useful in joins to handle NULL values?

IFNULL()

COALESCE()

ISNULL()

All of the above

None

11.

Which join includes all records from the right table and only matching records from the left table?

CROSS JOIN

RIGHT JOIN

INNER JOIN

LEFT JOIN

None

12.

Which type of join returns only matching rows from both tables?

CROSS JOIN

LEFT JOIN

INNER JOIN

RIGHT JOIN

None

13.

What is a foreign key?

An automatically generated value

A unique identifier for a table

A primary key of another table used to establish a relationship

A column that allows duplicate values

None

14.

How can you retrieve only matching records from two tables, ensuring no duplicate records appear in the final result set?

Use UNION ALL

Use CROSS JOIN

Use LEFT JOIN

Use INNER JOIN

None

15.

Which SQL keyword is used to perform a full outer join in MySQL?

CROSS JOIN

UNION of LEFT JOIN and RIGHT JOIN

FULL JOIN

FULL OUTER JOIN

None

16.

How can you combine two result sets that have the same structure but remove duplicate rows?

Use INNER JOIN

Use UNION ALL

Use UNION

Use CROSS JOIN

None

17.

Which SQL operator is used to combine the results of multiple SELECT queries?

UNION

JOIN

GROUP BY

MERGE

None

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