Union, Union All, Except, and Intersect

• The UNION operator combines the output of two query expressions into a single result set. Query expressions are executed independently, and their output is combined into a single result table.
• The purpose of the SQL UNION ALL command is also to combine the results of two queries together. The difference between UNION ALL and UNION is that, while UNIONonly selects distinct values, UNION ALLselects all values.The purpose of the SQL UNION ALL command is also to combine the results of two queries together. The difference between UNION ALL and UNION is that, while UNIONonly selects distinct values, UNION ALLselects all values.

·    The EXCEPT operator evaluates the output of two query expressions and returns the difference between the results. The result set contains all rows returned from the first query expression except those rows that are also returned from the second query expression.

·    The INTERSECT operator evaluates the output of two query expressions and returns only the rows common to each.