Why find_in_set works but IN clause

Question

I have code like this.

DELIMITER $$
    CREATE PROCEDURE `sp_deleteOrderData`(orderid BIGINT(11))
    BEGIN
        DECLARE shipmentnumbers VARCHAR(1000);
           


        

Answer 1

FIND_IN_SET searches a string inside a set of string separated by a comma.

• MySQL FIND_IN_SET

But you don't need to use GROUP_CONCAT to concatenate the rows to be used in the IN clause, try this,

SELECT  GROUP_CONCAT(a_cartonid) 
FROM    t_carton
WHERE   a_shipmentid IN
         (
            SELECT a_shipmentid
            FROM t_shipment 
            WHERE a_orderid = orderid
         )

or use JOIN

SELECT  GROUP_CONCAT(DISTINCT a.a_cartonid) 
FROM    t_carton a
        INNER JOIN
        (
            SELECT a_shipmentid
            FROM t_shipment 
            WHERE a_orderid = orderid
        ) b ON a.a_shipmentid = b.a_shipmentid

Answer 2

IN accepts a list or parameters to search, FIND_IN_SET accepts a string parameter containing a comma-separated list:

SELECT  1 IN (1, 2, 3, 4)

SELECT  FIND_IN_SET(1, '1,2,3,4')

If you try to apply IN to a comma-separated string, it will treat it as a single parameter and will match it as a whole:

SELECT  1 IN ('1,2,3,4')

Of course, the string '1' is not equal to the string '1,2,3,4' so the query above returns false.