Case in Where

Question

Case in Where

luissantos

SSCertifiable

Points: 7391
More actions
March 31, 2019 at 4:32 pm

#2253017

Hello community,
I have build this query and what i want is :
1. When fo.dprocesso not null then return all documents with this value
2.If fo.dprocesso is null then return all documents with the supplier name like ( fo.nome ).
<SQL>
Declare @Process as varchar(10)
Declare @Suppliername Varchar(60)
Set @Processo = ''
Set @Suppliername = 'weber'
SELECT cast(0 as bit) as marca, fo.*
FROM fo inner join fo2 on fo2.fo2stamp = fo.fostamp
where
foano = 2019 and fo2.u_tstamp = ''
AND (
(CASE WHEN fo.dprocesso IS NOT NULL THEN '%' + @Process + '%' ELSE '0' END ) = '1'
AND
(CASE WHEN fo.nome IS NOT NULL AND fo.dprocesso IS NULL THEN '%' + @Suppliername + '%' ELSE '0' END ) = '1'
)
</SQL>
something is missing because no value was return when @process not null, or, when @process is null and @Suppliername is not nul
Could someone help me.
Best regards,
Luis

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ChrisM@Work SSC Guru Points: 186127 More actions · Answer 1

Sometimes it helps to separate out the decision logic from the action logic, and a convenient way to do this is to put the decision logic into a CROSS APPLY block like this:

Declare @Processo as varchar(10)

Declare @Suppliername Varchar(60)

Set @Processo = ''

Set @Suppliername = 'weber'

SELECT cast(0 as bit) as marca, fo.*

FROM fo

INNER JOIN fo2

ON fo2.fo2stamp = fo.fostamp

CROSS APPLY (

SELECT MyFilter = CASE

WHEN fo.dprocesso IS NOT NULL THEN 1

WHEN fo.dprocesso IS NULL AND fo.nome IS NOT NULL THEN 2

WHEN fo.dprocesso IS NULL AND fo.nome IS NULL THEN 3

ELSE NULL END

) x

WHERE foano = 2019

AND fo2.u_tstamp = ''

AND (

(MyFilter = 1 AND fo.dprocesso LIKE '%' + @Processo + '%')

OR

(MyFilter = 2 AND fo.nome LIKE '%' + @Suppliername + '%')

OR

(MyFilter = 3)

)

^{“Write the query the simplest way. If through testing it becomes clear that the performance is inadequate, consider alternative query forms.” - Gail Shaw}

For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden

luissantos SSCertifiable Points: 7391 More actions · Answer 2

Hello Chris,

Great idea and example 🙂

it´s the first example with Cross Apply and separate decision logic that i saw, i will go to test it.

Many thanks for your reply.

Best regards,

Luis