How to use case statement to build dynamic where clause

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SQL-Server-2008R2

i have a table called master_unittype where uinttypeid and typename is there.
like
unittypeid-------------typename
1-------------------------kg
2-------------------------pc

now I have to select unittypeid,typename from this table using a condition.

some another query is returning 'kg','gm','pc' etc and i'm storing it a variable named
@usageunitName.

Now if @usageunitName='kg', i have to select unittypeid,typename from the master_unittype where typename='kg'
and
if @usageunitName='pc', i have to select unittypeid,typename from the master_unittype where typename='kg' or typename='pc'

What I have tried:

declare @usageunitName varchar(50);

select @usageunitName=typename from master_product inner join master_unit_type on master_product.productUnitTypeId=master_unit_type.unittypeid where productid=1;

select unittypeid,typename from master_unit_type where ((case when @usageunitName='kg' then (typename='kg')
when @usageunitName='pc' then (typename='kg' or typename='pc')
else typename=''
end));

Posted 11-Mar-16 8:20am

souvikcode

Updated 11-Mar-16 19:13pm

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ZurdoDev · Answer 1 · 2016-03-11T08:35:00

If you can combine the sql that would be best. For example, wherever you are SELECT @usageunitName = ... add that sql to this sql other sql in the where clause.

If you can't you have to do a dynamic sql statement, which is not preferred.

Change your sql to be a string

SQL

DECLARE @sql NVARCHAR (MAX)
SELECT @sql = 'SELECT ... FROM ... WHERE field1 = ' + @variable

EXEC (@sql)

Nigam,Ashish · Answer 2 · 2016-03-11T19:13:00

Solution 2

WHERE

CASE WHEN (@usageunitName IS NULL OR @usageunitName='')
THEN '1'
ELSE -- Your field Name
END = CASE WHEN (@usageunitName IS NULL OR @usageunitName='')
THEN '1'
ELSE @usageunitName
END

---- add another condition as per your requirment.

Ashish

Posted 11-Mar-16 19:13pm

Nigam,Ashish

Comments

souvikcode 12-Mar-16 11:03am

@usageunitName is going fine.I didn't ask case on that. I asked to use case on the last statement.

Nigam,Ashish 15-Mar-16 8:24am

I have given u a example you can put @usageunitName='pc' instead of '' or null and put your field in place of your field, and replace " AND " in to "OR"

souvikcode 15-Mar-16 8:29am

CASE WHEN (@usageunitName IS NULL OR @usageunitName='')
THEN '1'
ELSE -- Your field Name

This is you have written.
Can I put (myfield='pc' or myfield='kg') in place of "-- Your field Name"
on else cluse?