Mehdi9721 / DAC_SQL

sql_Most_imp_basic_for_revision

SUBQUERY

subquery type =>

1--> SCALAR
2--> MULTI ROW MULTI COLUMN
3--> CORRELATED

1--> SCALAR =>>

scalar subquery will return only 1row 1 col

select name,(select avg(sal) from emp) from emp;

2--> MULTI ROW MULTI COL

this subquery will return more than 1 row and 1 col,means multiple row with multi column can be returnd

key POINT

in (where) we can use "in()" for matching sub query with multiple row and col.

select * from emp where name in (select name from emp where name ='raju');

3--> correlated

it is a type of sub qurey which is related to its outer query

lets find employess having more salary than avg salary of there department

select * from employee e1 where sal> (select avg(sal) from employee e2 where e2.name=e1.name)

the subquery will depend on outer query and the outer query will return the whole record and inner query will match name with evrey record from the same department.