Added to the above Post... there are some techniques for writing the queries as follows
When you decide to use subqueries, consider the following facts and guidelines:
1.You must enclose subqueries in parentheses.
2.You can only use one expression or column name in the select list of a subquery that returns a value.
3.You can use subqueries in place of an expression as long as a single value or list of values is returned.
4.You cannot use subqueries on columns that contain text and image data types.
5.You can have as many levels of subqueries as you need—there is no limit.
6.The query that contains the subquery is usually called the outer query and a subquery is called an inner query.