MySQL variable used in where statement if variable set

Question

I would like to set a query up to filter by some user variables, if I choose to set them.

SET @item_number = 12345;

SELECT * FROM table 

    IF(@item_number IS NOT NULL, item_number = @item_number, NULL)

but based on my errors, I am not doing this properly.

Answer 1

Is this in a proc? Or are you trying to build up some dynamic SQL.

If in a proc you can build up dynamic SQL and that might be easiest.

A method that is likely to be inefficient (due to trying to work out whether an index would help the query) but easy to understand would possibly be:-

SET @item_number = 12345;

SELECT * FROM table WHERE (@item_number IS NULL OR item_number = @item_number);