MySQL

It allow us to add one or more column from one or more table in a single output. It follow some conditions to perform they are:

1. Number of column should be equal in both sides.
2. Both the matched column should have some type of data.

Syntax for Union

SELECT columnname1, columnname2
FROM table1
UNION DISTINCT | ALL
SELECT columnname1, columnname2
FROM table2
[WHERE CLAUSE
ORDER BY CLAUSE]

Example

SELECT ocuptn, sex
FROM studptin
UNION
SELECT fname,age
FROM studinfo ;

Default value use in union is distinct.

Example

SELECT fname,age
FROM studinfo
UNION ALL
SELECT ocuptn, sex
FROM studptin ;

The full output can be shown by all in union condition.

Example

SELECT ocuptn, sex
FROM studptin
UNION 
SELECT fname,age
FROM studinfo 
WHERE age>23
ORDER BY ocuptn;

Include the where and order b y condition in the above code.

Example

( SELECT ocuptn, sex
FROM studptin )
UNION 
( SELECT fname,age
FROM studinfo )
ORDER BY 2,1;

The type of order define in terms of the second select column name define in the code.