Answers for "union with where clause in sql server"

union and union all in sql server

/* UNION AND UNION ALL*/
union and union all operator in sql server are used to combine the result-set of
two or more select queries.
union remove duplicate rows, where as union all doesn't.
.e.g_
SELECT Column_List from Table_Name
UNION
SELECT Column_List from Table_Name
/--------------------------------------------/
.e.g_
SELECT Column_List from Table_Name
UNION ALL 
SELECT Column_List from Table_Name

/* UNION AND JOIN */
Union combine rows from 2 or more tables, where as 
join combine columns from 2 or more tables.

union in sql

UNION:
COMBINES THE RESULT OF 2 QUERY AND
REMOVES DUPLICATE ROWS AND
SORTS BY FIRST COLUMN