Difference between union and union all in SQL-Server- 2008?

UNION 

·         UNION is used to select distinct values from two tables.

·         Union are slow as compare to Union ALL

·         UNION similar to JOIN command.

·         When using the UNION command all selected columns need to be of the same data type.

Example

SELECT 'TEST'

      UNION

SELECT 'TEST'

RESULT:
 TEST


UNION ALL

·         UNION ALL will not eliminate duplicate rows; instead it just pulls all rows from all tables fitting your query specifics and combines them into a table.

·         UNION ALL is faster

Example

SELECT 'TEST'

      UNION ALL

SELECT 'TEST'

RESULT:
TEST
TEST