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Union vs Union All - MySQL Join

When working with multiple tables in MySQL, it's common practice to use the join keyword to combine data from two or more tables. However, you might also need to combine the results from two or more queries into a single result set. This can be achieved using the Union and Union All operators in MySQL. In this tutorial, we'll compare Union vs Union All and explain how to use them.

Syntax

The syntax for using the Union and Union All operators in MySQL is as follows:

SELECT column1, column2, ... FROM table1
UNION [ALL]
SELECT column1, column2, ... FROM table2;

The "UNION" keyword is used to combine the results of two or more SELECT statements into a single result set, while the optional "ALL" keyword is used to include all rows from both queries, even if they are duplicates.

Example

Let's say we have two tables: "employees" and "managers", and we want to combine the results of these tables into a single result set. Here's how we can implement it using the Union and Union All operators:

SELECT id, name, department FROM employees
UNION
SELECT id, name, department FROM managers;

This will give us a result set with the unique rows from both tables.

If we want to include all rows from both tables, even if they are duplicates, we can use the Union All operator:

SELECT id, name, department FROM employees
UNION ALL
SELECT id, name, department FROM managers;

Output

The output of the Union and Union All operators will depend on the data in the tables being joined. If there are duplicate rows, the Union operator will only return a single instance of each row, while the Union All operator will return all instances.

Explanation

In the example above, we used the Union and Union All operators to combine the results of two tables (employees and managers) into a single result set. The Union operator removes any duplicate rows, while the Union All operator includes all rows from both tables, even if they are duplicates.

Use

The Union and Union All operators can be used to combine the results of two or more queries into a single result set. This can be useful when querying multiple tables or when filtering data from the same table using different conditions.

Important Points

  • The Union operator removes duplicate rows, while the Union All operator includes all rows from both queries, even if they are duplicates.
  • The columns in both queries must be of the same data type and have the same number of columns.
  • The order of the columns in both queries must be the same.

Summary

In this tutorial, we compared Union vs Union All in MySQL and explained how to use them to combine the results of two or more queries into a single result set. We also discussed the syntax, example, output, explanation, use, and important points of the Union and Union All operators. With this knowledge, you can choose the right operator for your next MySQL query.

Union vs JoinUnique Key
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