Question

I had an issue in my stored procedure that needs to include rows or not depending on the value of a parameter

• if @var_exclude = 'Y' I need to show only rows that mytable.field1 = 'N'
• if @var_exclude = 'N' I need to show all rows

I’m using the following query but doesn’t work properly

My code is like

@var_exclude    varchar(1)

    select mytable.field1, mytable.field2, mytable.field3, mytable.field4,mytable.field5 
    from mytable
Where mytable.field6 is null
  and mytable.field1 is not null
  and (mytable.state = @paramstate or @paramstate = 'ALL')
  and  mytable.field1 = Case when @var_exclude= 'Y' Then 'N' Else @var_exclude End
End

I’m confused!

Answer 1

Your logic handling @var_exclude is wrong.

When you pass @var_exclude = 'Y', then your query basically gets resolved to:

select .....
from mytable
where mytable.field6 is null 
  and mytable.field1 is not null
  and (mytable.state = @paramstate or @paramstate = 'ALL')
  and mytable.field1 = 'N'

since in this case, the when @var_exclude= 'Y' Then 'N' part of your CASE clause is used.

If you pass anything else in, then you take the value you’re passing in; so if you pass in @var_exclude = 'N' then your query is resolved to:

select .....
from mytable
where mytable.field6 is null 
  and mytable.field1 is not null
  and (mytable.state = @paramstate or @paramstate = 'ALL')
  and mytable.field1 = 'N'

since in this case the Else @var_exclude of your CASE clause is used – and since @var_exclude = 'N', you get the exact same query as before….

I would probably write this procedure something like this:

CREATE PROCEDURE dbo.GetData 
     @paramstate VARCHAR(???),
     @var_exclude CHAR(1)
AS BEGIN 
   IF @var_exclude = 'N' THEN
      SELECT
         t.field1, t.field2, t.field3, t.field4, t.field5 
      FROM 
         dbo.mytable t
      WHERE 
         t.field6 IS NULL
         AND t.field1 IS NOT NULL
         AND (t.state = @paramstate OR @paramstate = 'ALL')

   ELSE
      SELECT
         t.field1, t.field2, t.field3, t.field4, t.field5 
      FROM 
         dbo.mytable t
      WHERE 
         t.field6 IS NULL
         AND t.field1 IS NOT NULL
         AND (t.state = @paramstate OR @paramstate = 'ALL')
         AND t.field1 = 'N'
END