SQL union allows you to combine the match result sets of two (or more than two) select queries into a single table.
SQL CASE expression is used as a kind of IF-THEN-ELSE statement.
SQL MINUS or EXCEPT operator work on two table expressions. The result set takes records from the first table expression, and then subtract out the ones that appear in the second table expression. If the second table expression includes the records which are not appear in the first table expression, these records will be ignored.
INTERSECT operator allows you to combine two table expressions into one and return a result set which consists of rows that appear in the results of both table expressions.