How to use union in sql

The UNION operation combines rows from different tables into a single result set, removing duplicate rows. The syntax format is: SELECT column_list FROM table1 UNION SELECT column_list FROM table2..., where table1 and table2 are the tables to be merged. The UNION operation requires that the participating tables have the same number of columns and data types, and that duplicate rows are removed.

UNION operation in SQL

What is the UNION operation?

The UNION operation combines rows from two or more tables into a single result set, thereby removing duplicate rows.

How to use UNION operation?

The syntax format of the UNION operation is:

<code class="sql">SELECT column_list
FROM table1
UNION
SELECT column_list
FROM table2
...</code>

Among them:

• column_list Specifies the columns to be retrieved from each table Columns
• table1, table2, ... are the tables to be merged

Example

For example, assume the students table and the teachers table have the following data:

students
John	20
Mary	22
Bob	25

teachers
Alice	30
David	35
Susan	40

Use the UNION operation to merge the two tables:

<code class="sql">SELECT name, age
FROM students
UNION
SELECT name, age
FROM teachers;</code>

The result will look like this:

##Alice30David35Susan40

name	age
John	20
Mary	22
Bob	25

##Notes

Tables participating in the UNION operation must have the same number of columns and data types.

• UNION operation does not retain duplicate rows. The
• UNION operation can be combined with other SQL operations, such as
WHERE
• and ORDER BY.

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