使用CASE添加到WHERE子句条件

Question

I have a stored procedure that accepts an optional @ID param. When the param is passed in, I want the WHERE statement to include something like id = @ID, otherwise, when @ID is null, I don't want it to be filtered.

For example:

@ID BIGINT = NULL

SELECT * from myTable
WHERE 
CASE
    WHEN @ID IS NOT NULL THEN mytable.id = @ID
END

I am running this in SQL server 2016 and it says bad syntax near mytable.id = @ID. Can CASE be used in this way or should I try a different SQL method for this?

The only other option I considered to accomplish this was by using IF conditions in my stored procedure, but that didn't seem possible either based on my searches.

Answer 1

CASE is an expression, not a statement. It is not used to control flow like this and it will not work.

Your logic would need to be something like this.

Where mytable.id = ISNULL(@ID, mytable.id)

I should caution you that this pattern can lead to some poor performance. For a more detailed explanation and some other options you should check out this article. http://www.sqlinthewild.co.za/index.php/2009/03/19/catch-all-queries/

Answer 2

A bad-performance approach would be:

WHERE ISNULL(@ID,mytable.id) = mytable.id

A better-performance approach would be:

 if(@ID IS NULL)
   select * from ... without the WHERE condition
else
    do your query with the condition mytable.id = @ID

Or build the query dynamically in the stored proc and execute it through sp_executesql passing parameters

Note: If the table is small enough, stick to simplicity and use the first option.