Answer Posted / minor kunju

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Here is The Difference

Though the HAVING clause specifies a condition that is
similar to the purpose of a WHERE clause, the two clauses
are not interchangeable. Listed below are some differences
to help distinguish between the two:

1. The WHERE clause specifies the criteria which individual
records must meet to be selcted by a query. It can be used
without the GROUP BY clause. The HAVING clause cannot be
used without the GROUP BY clause.

2. The WHERE clause selects rows before grouping. The
HAVING clause selects rows after grouping.

3. The WHERE clause cannot contain aggregate functions. The
HAVING clause can contain aggregate functions.




The HAVING clause allows you to filter the results of
aggregate functions,
such as COUNT() or AVG() or SUM(), or MAX() or MIN(), just
to name a few.

HAVING provides you a means to filter these results in the
same query,

as opposed to saving the results of a WHERE clause SQL
statement to a temporary table

and running another query on the temporary table results to
extract the same results.


Follow The Below Example This Will Clear Up

Go





Create table Test_Where_Having

(id int identity,[Name] varchar(20),[Age] int,Amount int)

Go

insert into Test_Where_Having

select 'Abc',20,100

union all

select 'Def',30,100

union all

select 'Ghi',52,500

union all

select 'Jkl',30,80

union all

select 'Mno',40,600

union all

select 'Pqr',60,500

union all

select 'Pqr',60,500

union all

select 'Abc',20,500
Go

--They both are use to exclude rows from the resultset,

--but "where" is to filter the original set

--and "having" is in case you are grouping.

select [Name],[Age] from Test_Where_Having

where Age>30

--Output

Name Age

-------------------- -----------

Ghi 52

Mno 40

Pqr 60

Pqr 60





select [Name],[Age],Sum(Amount) As Total from
Test_Where_Having

group by [Name],[Age]

having Sum(Amount)>400

--Output

Name Age Total

-------------------- ----------- -----------

Abc 20 600

Mno 40 600

Ghi 52 500

Pqr 60 1000





--For Below Case These Queries Are Same As per Performance
(Cost Of Query) And result basis

select [Name],[Age],Sum(Amount) As Total from
Test_Where_Having

where Age>30

group by [Name],[Age]

select [Name],[Age],Sum(Amount) As Total from
Test_Where_Having

group by [Name],[Age]

having Age>30






--For Below Case These Queries Are Same As per Performance
(Cost Of Query) And result basis

select [Name],[Age] from Test_Where_Having

where Age>30

group by [Name],[Age]

select [Name],[Age] from Test_Where_Having

group by [Name],[Age]

having Age>30












--WHERE is used to filter rows. HAVING is usually used to
filter rows after performing an aggregation.

--Below Query is incorrect While using aggregate with where
clause

select [Name],[Age],Sum(Amount) As Total from
Test_Where_Having

where Sum(Amount)>30

group by [Name],[Age]

--U can use the above with Having

select [Name],[Age],Sum(Amount) As Total from
Test_Where_Having

group by [Name],[Age]

having Sum(Amount)>30

--Output

Name Age Total

-------------------- ----------- -----------

Abc 20 600

Def 30 100

Jkl 30 80

Mno 40 600

Ghi 52 500

Pqr 60 1000











--You can't use HAVING unless you also use GROUP BY.

--Ie below Query is incorrect

select [Name],[Age],Sum(Amount) As Total from
Test_Where_Having

having Sum(Amount)>30






--One limitation when you use the HAVING clause as compare
to WHERE clause.

-- Having clause only supports the Grouped Columns &
Aggregation filter..

--Where there is a column level filter then always use the
Where clause,

--Use Having clause only for Aggregation filter.

--For Example Below U cant use Amount column in Having
Clause because it is not in grouped columns

select [Name],[Age] from Test_Where_Having

group by [Name],[Age]

having Amount>30


--For The Above Case U can Use Where Clause

select [Name],[Age] from Test_Where_Having

where Amount>30

group by [Name],[Age]

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