Question

I’m having some trouble with the following sproc

Create PROCEDURE GetMatchingUsers
@id int = NULL,
@lastName varchar(50) = NULL,
@firstName varchar(50) = NULL
AS
BEGIN

 SET NOCOUNT ON

 DECLARE @q nvarchar(4000),
 @paramlist  nvarchar(4000)  

    SELECT @q = 'SELECT Id
  , LastName
  , FirstName '
 SELECT @q = @q + 'FROM Users WHERE 1 = 1' 

 IF ISNULL(@id, '')  <> ''                                 
  SELECT @q = @q + ' AND Id = ' + Cast(@id as varchar)
 IF ISNULL(@lastName, '')  <> ''                                           
  SELECT @q = @q + ' AND LastName like ''' + @lastName + '%''' 
 IF ISNULL(@firstName, '')  <> ''                                           
  SELECT @q = @q + ' AND FirstName like ''' + @firstName + '%'''   

 SELECT @q = @q + ' ORDER BY LastName, FirstName '

 --PRINT @q

 SELECT @paramlist = '
  @id int = NULL,
  @lastName varchar(50) = NULL,
  @firstName varchar(50) = NULL'

 EXEC sp_executesql @q, @paramlist,                               
   @id,
   @lastName,
   @firstName

I was wonder why the following if statement is not considered true if i pass 0 as an id

IF ISNULL(@id, '')  <> ''                                 
    SELECT @q = @q + ' AND Id = ' + Cast(@id as varchar)

Thanks for any help

Answer 1

That is pretty weird – it probably has something to do with the fact that you are mixing up an int and a string literal. It seems more straightforward to do if @id is null or if @id is not null depending on your requirements

I reproduced this with a simple example (I changed <> to = to make the logic a little more obvious):

declare @id int
set @id = 0

if isnull(@id, '') = '' 
  print 'true'
else
  print 'false'

You would expect this to print ‘false’, but it prints ‘true’. If you set the value of @id to 1, it then behaves as expected.