Introduction to MySQL Joins

Introduction to MySQL Joins

In MySQL, a join is used to combine rows from two or more tables based on a related column between them. This allows us to retrieve data from multiple tables in a single query, making it a powerful tool for data analysis and reporting. There are different types of joins in MySQL, each serving a specific purpose. In this article, we will explore some common MCQ questions on MySQL joins along with their answers and explanations.

Question 1:

What is a join in MySQL?

1. A function that combines two or more strings
2. A query that retrieves data from multiple tables based on a related column
3. A command used to create a new table
4. An operator used to perform mathematical calculations

Answer: b) A query that retrieves data from multiple tables based on a related column

Explanation: A join in MySQL is a query that combines rows from two or more tables based on a related column between them. It allows us to retrieve data from multiple tables in a single query.

Question 2:

Which join returns all rows from both tables, regardless of whether there is a match?

1. INNER JOIN
2. LEFT JOIN
3. RIGHT JOIN
4. FULL JOIN

Answer: d) FULL JOIN

Explanation: A FULL JOIN returns all rows from both tables, regardless of whether there is a match or not. If there is no match, NULL values are returned for the missing columns.

Question 3:

Which join returns only the rows that have matching values in both tables?

1. INNER JOIN
2. LEFT JOIN
3. RIGHT JOIN
4. FULL JOIN

Answer: a) INNER JOIN

Explanation: An INNER JOIN returns only the rows that have matching values in both tables. It excludes the rows that do not have a matching value in the specified column.

Question 4:

Which join returns all rows from the left table and the matching rows from the right table?

1. INNER JOIN
2. LEFT JOIN
3. RIGHT JOIN
4. FULL JOIN

Answer: b) LEFT JOIN

Explanation: A LEFT JOIN returns all rows from the left table and the matching rows from the right table. If there is no match, NULL values are returned for the missing columns in the right table.

Question 5:

Which join returns all rows from the right table and the matching rows from the left table?

1. INNER JOIN
2. LEFT JOIN
3. RIGHT JOIN
4. FULL JOIN

Answer: c) RIGHT JOIN

Explanation: A RIGHT JOIN returns all rows from the right table and the matching rows from the left table. If there is no match, NULL values are returned for the missing columns in the left table.

Question 6:

Which join combines rows from two or more tables based on a related column, and includes all rows from both tables?

1. INNER JOIN
2. LEFT JOIN
3. RIGHT JOIN
4. FULL JOIN

Answer: d) FULL JOIN

Explanation: A FULL JOIN combines rows from two or more tables based on a related column and includes all rows from both tables, regardless of whether there is a match or not.

Question 7:

Which join is used to combine rows from two or more tables based on a related column?

1. UNION JOIN
2. COMBINE JOIN
3. JOIN
4. RELATED JOIN

Answer: c) JOIN

Explanation: The JOIN keyword is used to combine rows from two or more tables based on a related column. It is the most common type of join used in MySQL.

Question 8:

Which join returns the Cartesian product of the two tables?

1. INNER JOIN
2. CROSS JOIN
3. OUTER JOIN
4. SELF JOIN

Answer: b) CROSS JOIN

Explanation: A CROSS JOIN returns the Cartesian product of the two tables, which means it combines each row from the first table with each row from the second table.

Question 9:

Which join is used to join a table with itself?

1. INNER JOIN
2. LEFT JOIN
3. RIGHT JOIN
4. SELF JOIN

Answer: d) SELF JOIN

Explanation: A SELF JOIN is used to join a table with itself. It is useful when we want to combine rows from the same table based on a related column.

Question 10:

Which join is the most common type of join used in MySQL?

1. UNION JOIN
2. COMBINE JOIN
3. JOIN
4. RELATED JOIN

Answer: c) JOIN

Explanation: The JOIN keyword is the most common type of join used in MySQL. It is used to combine rows from two or more tables based on a related column.

These were some MCQ questions on MySQL joins along with their answers and explanations. Understanding joins is essential for working with multiple tables in MySQL and performing complex data analysis.

I hope this article has helped you in gaining a better understanding of MySQL joins. If you have any further questions, feel free to ask!