Union All Operator

The SQLite UNION ALL operator is used to combine the result of two or more SELECT statement without ignoring the duplicate rows.

In SQLite UNION ALL, the resultant table also includes the duplicate values. Otherwise, the same rule applies as Union.

Syntax:

SELECT expression1, expression2, ... expression_n  

FROM tables  

[WHERE conditions]  

UNION ALL  

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 ALL.

SELECT ID FROM STUDENT  

UNION ALL   

SELECT ID FROM DEPARTMENT;  

Output:

Example2: UNION ALL 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 ALL Clause:

SELECT EMP_ID, NAME, DEPT FROM STUDENT INNER JOIN DEPARTMENT  

ON STUDENT.ID = DEPARTMENT.EMP_ID  

UNION ALL  

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

ON STUDENT.ID = DEPARTMENT.EMP_ID; 

Output: