What are the guidelines for using SUB-QUERIES?

Answer

Following things need to be kept in mind when you write sub-queries:

* Caution should be taken with simple sub-query, especially when a normal value operator is used on the results of a sub-query, only one field must be returned

* If you want to check for the existence of a single value within a set of other values, use the IN keyword as an operator upon the result set from a sub-query.

Example of a Sub-Query:

Code:

SELECT name FROM students

     WHERE stud_id = (SELECT stud_id FROM class 

              WHERE last_name='abc'

                  AND first_name='xyz');