What is better, dynamic SQL or where case?

问题

I need to create a stored procedure which takes 12 arguments and the query is filtered with a different combination of this arguments. All 12 arguments are not mandatory as if I pass 3 or 5 or 12 arguments depends on search inputs entered by user.

I can create 2 ways, either using a dynamic SQL query or using 'Case where' statements. Example of these queries are as below:

Dynamic Query

DECLARE @sql VARCHAR(MAX) 
DECLARE @condition VARCHAR(MAX)=''
Declare @var1 varchar(10)
Declare @var2 varchar(10)
Declare @var3 varchar(10) 
SET  @sql='SELECT * FROM TableDemo1 TD1 WITH(NOLOCK)
 INNER JOIN TableDemo2 TD2 ON TD1.Column1=TD2.Column2'
if(@var1 <>0 and @var1 is not null)
begin
    if(@condition<>'')
    begin
        set @condition=@condition + ' and TD1.columnTest1='+@var1)
    end
    else
    begin
        set @condition=' where TD1.columnTest1='+@var1
    end
end
if(@var2 <>0 and @var2 is not null)
begin
    if(@condition<>'')
    begin
        set @condition=@condition + ' and TD2.columnTest2='+@var2)
    end
    else
    begin
        set @condition=' where TD2.columnTest2='+@var2
    end
end

if(@var3 <>0 and @var3 is not null)
begin
    if(@condition<>'')
    begin
        set @condition=@condition + ' and TD1.columnTest3='+@var3)
    end
    else
    begin
        set @condition=' where TD1.columnTest3='+@var3
    end
end
SET @sql=@sql+@condition
EXEC(@sql)

Query with CASE WHERE

Declare @var1 varchar(10)
Declare @var2 varchar(10)
Declare @var3 varchar(10)
SELECT *
FROM TableDemo1 TD1 WITH(NOLOCK)
    INNER JOIN TableDemo2 TD2 ON TD1.Column1=TD2.Column2
WHERE
  (CASE WHEN   
    (@var1<>0 and @var1 is not null)   
    THEN  
    CASE WHEN TD1.columnTest1=@var1 THEN 1 ELSE 0 END  
    ELSE 1 END)=1  
  AND   
  (CASE WHEN  
    (@var2<>0 and @var2 is not null)   
    THEN  
    CASE WHEN TD2.columnTest2=@var2 THEN 1 ELSE 0 END  
    ELSE 1 END)=1  
  AND
  (CASE WHEN
    (@var3<>0 AND @var3 IS NOT NULL)
    THEN
    CASE WHEN TD1.columnTest3 = @var3
    THEN 1 ELSE 0 END
    ELSE 1 END) =1

This is just part of my stored procedure, there are 7-8 tables with joins and as above in query variety in conditions.

If I use a dynamic query, SQL Server will have to create an execution plan every time, but if I use 'case where' it also makes the query slow.

I am aware of disadvantages of dynamic SQL, but which technique I should use?

回答1:

Generally it depends, but most often I use dynamic queries as a last resort. Regarding your question, I would most probably go with the CASE solution, but I think your CASE expressions are unnecessarily complicated. I would replace the WHERE clause with something like this:

...
WHERE
    TD1.columnTest1 = COALESCE(NULLIF(@var1, 0), TD1.columnTest1)
    AND   
    TD2.columnTest2 = COALESCE(NULLIF(@var2, 0), TD2.columnTest2)
    AND   
    TD1.columnTest3 = COALESCE(NULLIF(@var3, 0), TD1.columnTest3)

With proper indexing this shouldn't be too slow.

回答2:

The dynamic query will lead to an index scan.

The case will lead to a seq scan (i.e. read the whole table).

So definitely go with the dynamic query.

回答3:

In my experience a dynamic where clause provides better performance. Especially over large datasets.

And a very good explanation is in Catch All Queries.

回答4:

I have used the option "Andriy M" posted using coalesce and nullif functions.

But this option works only with the '=' operator, yet to find how to use it with other conditions, one example is using the 'IN' keyword.

TD1.columnTest1 = (
    CASE 
        WHEN (
            ( TD1.columnTest1 
                IN (
                    SELECT item FROM dbo.Splitfunction(@comaSepValues,',')
                )
            ) 
            OR 
            NULLIF(@PlaceTypeCode,'') IS NULL 
        ) THEN columnTest1
        ELSE NULL 
    END
)

Let me know if this works or not.