Database System-Nested Subquery

1. NESTED SUBQUERY

2. PREPARED BY
Ms.R.Ragavi -III-B.Sc - Information Technology
UNDER THE GUIDANCE OF
Mrs.P.Anusha M.Sc(IT).,M.Phil.,D.P.T.T.,(Ph.D).,
Assistant professor,
Department of Information Technology,
Bon secours college for women,
Thanjavur.

3. DEFINE NESTED SUBQUERY
• A Subquery or inner query or a Nested query is
a query within another SQL query and
embedded within the WHERE clause.
• A Common use of subqueries is to perform test
for set membership, make set comparisons, and
determine set cardinality by nesting of
subqueries in the WHERE clause.

4. USES
• A subquery is used to return data that will be used in
the main query as a condition to further restrict the
data to be retrieved.
• Subquery can be used with the SELECT , INSERT,
UPDATE , and DELETE statements along with the
operators like =,<,>,>=,<=, IN BETWEEN etc.
• Sub queries must be enclosed within parentheses.

5. • A subquery can have only one column in the SELECT
clause, unless multiple columns are in the main query for
the sub query to compare its selected columns.
• An ORDER BY COMMAND cannot to used in a
subquery.
• SQL provides a mechanism for nesting subqueries.

6. CUSTOMER
ID
NAME AGE ADDRESS SALARY
001 ANITHA 30 CHIDAMBARAM 20,000
002 SIVAKAMI 25 KUMBAKONAM 24,000
003 ALAMELU 26 NEYVELI 26,000
004 GEETHA 45 THANJAVUR 38,000
005 RANI 35 TRICHY 20,000
006 MALATHI 36 BANGALORE
007 GOPI 29 KERALA

7. SYNTAX
• Select column name from table name where column name
operator(select column name from table name where);

8. EXAMPLE
Select * from customers where customer_id IN (select customers_id
from customers where salary >=25000;
Customer _id Name Age Address Salary
003 Alamelu 26 Neyveli 26000
004 Geetha 45 Thanjavur 38000