1.The SELECT query of a subquery is alwaysenclosed in parentheses
2.View created by using a subquery cannot beupdated.
3.The ntext, text, and image data types cannot beused in the select list of sub queries
4.If a table appears only in a subquery and not inthe outer query, then columns from that table cannot be included in the output
Example related to Subqueries
·Subquerieswith IN and NOT IN:
Example 1: SELECT city FROMtblCity WHERE ID NOTIN (SELECT CityID FROMtblState WHERE StateId ='25')
Example 2: SELECT city FROMtblCity WHERE ID IN(SELECT CityID FROM tblState WHEREStateId = '25')
·Subquerieswith comparison operators.
Comparison operators can be used (like <, >, =,!> etc). Sub queries used with comparison operators must return a singlevalue rather than a list to avoid error. Hence the nature of the database mustbe knows before executing such sub queries.
Example : SELECT sName FROMtblEmployee WHERE nSalary > '5000'
·Subquerieswith Exists and NOT Exists.
A subquery with Exist does not really return any data; itreturns TRUE or FALSE.
Example 1: SELECT sName FROMtblEmployee WHERE NOTEXISTS(SELECT
* FROM tblCompany WHERE nID = 'emp0004'AND Name = 'E Vergis')
Example 2: SELECT sName FROMtblEmployee WHERE EXISTS(SELECT *
FROM tblCompany WHEREnID = 'emp0004'AND Name = 'E Vergis')