Question

I come from frontend background and I am trying to write a stored proc that can accept null parameter. Here’s a simplified version:

CREATE PROCEDURE get_item(IN item_id INT(11))
BEGIN

SELECT * FROM item a WHERE a.item_id = IF(item_id IS NULL, a.item_id, item_id);

END;;

So I want to SELECT everything if item_id is null, otherwise, I want the WHERE clause to apply. Is this the way to do it? It seems to work, but I am not sure if there is a better way.

I think I can also write it like this:

SELECT * FROM item a WHERE ((item_id IS NULL) OR (a.item_id = item_id));

Answer 1

SELECT * FROM item a WHERE a.item_id = IF(item_id IS NULL, a.item_id, item_id);

is a performance killer: instead of using no WHERE, it will evaluate your IF for every row, as it is not a constant expression.

SELECT * FROM item a WHERE ((item_id IS NULL) OR (a.item_id = item_id));

is a good way, as the query planner will see, that the WHERE evaluates to a contant expression of TRUE

My way would be to put an IF into the stored procedure top level, that decides between two queries, one having a WHERE, the other not. While this is quite verbouse, it is also quite readable.