Case Statement in Where Clause on a Parameter

Hello I have the below store proc
declare @po_start_date varchar(15)
declare @po_end_date varchar(15)

SELECT
     ex.vendor_code,
     ex.program,
     ex.Po_num,
     ex.date_create,
     ex.Printed_Date,
     ex.status,
     ex.po_item_No,
     ex.Supplier_pn,
     ex.price,
     ex.unit_of_meas,
     ex.extd_cost,
     ex.quantity,
     ex.open_qty,
     ex.baseline_date,
     ex.[Current_Date],
     ex.nomenclature,
     ex.customer_no,
     ex.control_and_item,
     ex.need_date,
     ex.fax,
     ex.state,
     ex.vendor_name,
     ex.vendor_phone,
     ex.vendor_contact,
     ex.disposition,
     ex.ship_via,
     ex.need_date3,
     ex.a_status,
     ex.data,
     ex.next_higher_assy

FROM
     expeditetbl1 ex 
     left join
(
    select 
        emp_num, pGM_CODES 
    from  exp_dummytbl
    group by emp_num, pGM_CODES
) 
Q ON ex.program = Q.pGM_CODES

where  Q.emp_num='092'
     and ex.vendor_code IS NOT null
     and ex.open_qty <> 0
     and (ex.program ='632'
     and Case  
		When @po_start_date <> ''
	    Then (ex.[Current_Date] > = @po_start_date)
		END 

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Iam trying to put a case condition on the param start date to check to see if its empty string or the user has passed a value.Iam getting an incorrect syntax on my code.Please help.
Star79Asked:
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Jim HornMicrosoft SQL Server Developer, Architect, and AuthorCommented:
Instead of CASE just use WHERE (what to do if NULL or '' OR expression).
If empty string means return all rows...
SELECT blah, blah, blah
FROM your_table
WHERE (ISNULL(@po_start_date, '') = '' OR ex.[Current_Date] > = @po_start_date)

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If empty string means something different, tell us.

btw I have an article out there on SQL Server CASE Solutions, with a wompload of examples, if it helps.
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dsackerContract ERP Admin/ConsultantCommented:
First, this is not a stored proc. This is a script.

Secondly, you can't put a command within a CASE statement. This:
Then (ex.[Current_Date] > = @po_start_date)

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... is not allowed.

Just guessing, but perhaps your line could read something like:
 and (ex.program ='632'
     and ex.[Current_Date] > CASE
		When ISNULL(@po_start_date, '') = '' Then GETDATE()
		WHEN ISDATE(@po_start_date) = 0 THEN GETDATE()
		ELSE CONVERT(datetime, @po_start_date)
	END

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CASE only renders a value. It cannot take action. If you require a @po_start_date, you'll need to validate that at the top of your script (or your proc, if that is what this will eventually become).
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Racim BOUDJAKDJIDatabase Architect - Dba - Data ScientistCommented:
Alternatively to Jim's solution..
My guess is that the OP only wants to make the parameter optional.
WHERE
.....
ex.[Current_Date] > = isnull(@po_start_date, ex.[Current_Date] )

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Tip: if the @po_start_dateparameter is null then only the > applies, else only the equality applies and annuls the condition predicate.

Hope this helps.
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HainKurtSr. System AnalystCommented:
here it is

where ex.[Current_Date] >= isnull(@po_start_date, ex.[Current_Date])

oops, it is already posted :)
0
Scott PletcherSenior DBACommented:
Nope, that ISNULL() approach involving a column can be awful for performance.  You're forcing the column value to be compared to itself for every row.

The better coding approach is:
   and (ISNULL(@po_start_date, '') = '' OR @po_start_date = ex.[Current_Date])
because SQL can, and very often will, 'short-circuit' before the last comparison.


For example, try the code below against any table with a "name" column, and look at the query plans.  For the first plan, you won't (shouldn't) see a 'Predicate'/comparison at all.  With the second, you'll see that it does need a Predicate/comparison.


declare @name varchar(128)

--no predicate, because SQL can strip it.
select *
from dbo.table_with_name_column
where isnull(@name, '') = '' or name = @name --proper method

--with predicate, because SQL can't strip it.
select *
from dbo.table_with_name_column
where name = isnull(@name, name) --improper method, do not use!
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HainKurtSr. System AnalystCommented:
agree with ScottPletcher

and (ISNULL(@po_start_date, '') = '' OR @po_start_date = ex.[Current_Date])

or this one

and (ISNULL(@po_start_date, '') = '' OR @po_start_date = ex.[Current_Date])

^^^ looks best option, which I always used in my old asp portals :) after getting values from a search form on a webpage, I used one query like

sql="select ...
where ...
((':param1'='') or (column1=':param1')) and
((':param2'='') or (column2=':param2')) and
...
((':paramN'='') or (columnN=':paramN'))"

then

sql.replace(":param1",param1)
sql.replace(":param2",param2)
...
sql.replace(":paramN",paramN)

then run sql in db...
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Microsoft SQL Server 2005

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