Union Operator

SQLite UNION Operator is used to combine the result set of two or more tables using SELECT statement. The UNION operator shows only the unique rows and removes duplicate rows.

While using UNION operator, each SELECT statement must have the same number of fields in the result set.

Syntax:

SELECT expression1, expression2, ... expression_n  

FROM tables  

[WHERE conditions]  

UNION  

SELECT expression1, expression2, ... expression_n  

FROM tables  

[WHERE conditions]; 

Example:

We have two tables “STUDENT” and “DEPARTMENT”.

The “STUDENT” table is having the following data:

The “DEPARTMENT” table is having the following data:

Example1: Return Single Field

This simple example returns only one field from multiple SELECT statements where the both fields have same data type.

Let’s take the above two tables “STUDENT” and “DEPARTMENT” and select id from both table to make UNION.

SELECT ID FROM STUDENT  

UNION  

SELECT ID FROM DEPARTMENT;  

Output:

Example2: Union with Inner and Outer Join

Let’s take the above two tables “STUDENT” and “DEPARTMENT” and make an inner join and outer join according to the below conditions along with UNION Clause:

SELECT EMP_ID, NAME, DEPT FROM STUDENT JOIN DEPARTMENT  

ON STUDENT.ID = DEPARTMENT.EMP_ID  

UNION  

SELECT EMP_ID, NAME, DEPT FROM STUDENT LEFT OUTER JOIN DEPARTMENT  

ON STUDENT.ID = DEPARTMENT.EMP_ID;  

Output: