Sub Queries-

Three basic rules only.

Where you can place sub query?
3 places where you can place your sub query:
SELECT ----- FROM
FROM   ----- WHERE
WHERE  ----->

SELECT ----- FROM
_____________________
(sub query can only return single value & no alias to value returned is required)

Correct:
_________

(select max(val) from abc where ---) Ex output: 10
(select top 1 val from abc where ----) Ex output: abctext

Wrong:
_________
(select val from abc where ----) and result is returning multple rows:

Ex. ouput of above query:
val
___
12
32
45
6
45

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