Set Operations in SQL

SQL supports few Set operations to be performed on table data. These are used to get meaningful results from data, under different special conditions.

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Union

UNION is used to combine the results of two or more Select statements. However it will eliminate duplicate rows from its result set. In case of union, number of columns and datatype must be same in both the tables.

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Example of UNION

The First table,

ID	Name
1	abhi
2	adam

The Second table,

ID	Name
2	adam
3	Chester

Union SQL query will be,

select * from First
UNION
select * from second 

The result table will look like,

ID	NAME
1	abhi
2	adam
3	Chester

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Union All

This operation is similar to Union. But it also shows the duplicate rows.

Example of Union All

The First table,

ID	NAME
1	abhi
2	adam

The Second table,

ID	NAME
2	adam
3	Chester

Union All query will be like,

select * from First
UNION ALL
select * from second 

The result table will look like,

ID	NAME
1	abhi
2	adam
2	adam
3	Chester

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Intersect

Intersect operation is used to combine two SELECT statements, but it only retuns the records which are common from both SELECT statements. In case of Intersect the number of columns and datatype must be same. MySQL does not support INTERSECT operator.

Example of Intersect

The First table,

ID	NAME
1	abhi
2	adam

The Second table,

ID	NAME
2	adam
3	Chester

Intersect query will be,

select * from First
INTERSECT
select * from second 

The result table will look like

ID	NAME
2	adam

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Minus

Minus operation combines result of two Select statements and return only those result which belongs to first set of result. MySQL does not support INTERSECT operator.

Example of Minus

The First table,

ID	NAME
1	abhi
2	adam

The Second table,

ID	NAME
2	adam
3	Chester

Minus query will be,

select * from First
MINUS
select * from second 

The result table will look like,

ID	NAME
1	abhi