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.

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

COALESCE()

IFNULL()

All of the above

ISNULL()

None

Which type of join can result in a Cartesian product?

RIGHT JOIN

INNER JOIN

LEFT JOIN

CROSS JOIN

None

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

To specify the condition for joining tables

To sort query results

To combine duplicate records

To remove NULL values

None

What is the difference between UNION and UNION ALL?

UNION ALL removes duplicate rows, while UNION includes them

There is no difference

UNION only works with INNER JOIN

UNION removes duplicate rows, while UNION ALL includes them

None

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

Only matching rows

All rows from the right table

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

No results

None

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

LEFT JOIN

CROSS JOIN

RIGHT JOIN

INNER JOIN

None

What does the USING clause do in a JOIN?

Creates a new index on the table

Specifies a common column between two tables without prefixing table names

Removes duplicate rows

Combines multiple columns into a single key

None

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

Only matching rows are shown

The query fails

No rows are returned

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

None

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

SELECT * FROM customers JOIN orders;

SELECT * FROM customers, orders;

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

SELECT * FROM customers CROSS JOIN orders;

None

10.

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

Use CROSS JOIN

Use INNER JOIN

Use UNION

Use UNION ALL

None

11.

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

UNION

JOIN

GROUP BY

MERGE

None

12.

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

Use LEFT JOIN

Use INNER JOIN

Use CROSS JOIN

Use UNION ALL

None

13.

What is a foreign key?

A primary key of another table used to establish a relationship

An automatically generated value

A unique identifier for a table

A column that allows duplicate values

None

14.

What does a CROSS JOIN do?

Returns all possible combinations of rows from two tables

None of the above

Joins two tables and excludes NULL values

Matches rows from both tables based on a common column

None

15.

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

LEFT JOIN

INNER JOIN

RIGHT JOIN

CROSS JOIN

None

16.

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

UNION of LEFT JOIN and RIGHT JOIN

CROSS JOIN

FULL OUTER JOIN

FULL JOIN

None

17.

What is the primary purpose of using joins in MySQL?

To create new tables

To delete duplicate records

To improve indexing performance

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

None

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