techguy Said..
As I know subqueries can be classified as many ways
# With aliases. For more information, see Subqueries with Aliases.
# With IN or NOT IN. For more information, see Subqueries with IN and Subqueries with NOT IN.
# In UPDATE, DELETE, and INSERT statements. For more information, see Subqueries in UPDATE, DELETE, and INSERT Statements.
# With comparison operators. For more information, see Subqueries with Comparison Operators.
# With ANY, SOME, or ALL. For more information, see Comparison Operators Modified by ANY, SOME, or ALL.
# With EXISTS or NOT EXISTS. For more information, see Subqueries with EXISTS and Subqueries with NOT EXISTS.
# In place of an expression. For more information, see Subqueries Used in Place of an Expression.