MySQL · December 20, 2023

MySQL Tip: Use UNION operator to combine result sets of two or more SELECT statements.

MySQL Tip: Use UNION operator to combine result sets of two or more SELECT statements

MySQL is a popular open-source relational database management system that is widely used for various web applications. It offers a wide range of features and functionalities to handle complex data operations efficiently. One such feature is the UNION operator, which allows you to combine the result sets of two or more SELECT statements into a single result set.

Understanding the UNION operator

The UNION operator in MySQL is used to combine the result sets of two or more SELECT statements into a single result set. It eliminates duplicate rows from the combined result set by default. The syntax for using the UNION operator is as follows:

SELECT column1, column2, ...
FROM table1
UNION
SELECT column1, column2, ...
FROM table2;

Here, the SELECT statements can have different columns, but the number of columns in each SELECT statement must be the same. The data types of corresponding columns must also be compatible.

Benefits of using the UNION operator

The UNION operator offers several benefits when it comes to combining result sets:

  • Combining data from multiple tables: The UNION operator allows you to combine data from different tables into a single result set. This can be useful when you need to fetch data from multiple tables that have a similar structure.
  • Eliminating duplicate rows: By default, the UNION operator eliminates duplicate rows from the combined result set. This can be handy when you want to retrieve unique records from multiple tables.
  • Flexible filtering and sorting: You can apply filtering and sorting operations on each SELECT statement individually before combining the result sets using the UNION operator. This gives you the flexibility to manipulate the data as per your requirements.

Example usage of the UNION operator

Let's consider an example where we have two tables: customers and orders. The customers table contains information about the customers, and the orders table contains information about the orders placed by those customers. We can use the UNION operator to combine the result sets of two SELECT statements to fetch the customer names and order details in a single result set.

SELECT customer_name
FROM customers
UNION
SELECT order_details
FROM orders;

This query will return a result set with the customer names and order details combined, eliminating any duplicate rows.

Conclusion

The UNION operator in MySQL is a powerful tool that allows you to combine the result sets of two or more SELECT statements into a single result set. It provides flexibility in fetching and manipulating data from multiple tables. By using the UNION operator, you can efficiently retrieve unique records and perform complex data operations. Incorporating the UNION operator in your MySQL queries can enhance the functionality and efficiency of your database operations.

Summary:

The UNION operator in MySQL allows you to combine the result sets of two or more SELECT statements into a single result set. It offers benefits such as combining data from multiple tables, eliminating duplicate rows, and providing flexible filtering and sorting options. To learn more about Server.HK and its VPS hosting services, visit Server.HK.

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