Why find_in_set works but IN clause - mysql

Question

I have code like this.
DELIMITER $$
CREATE PROCEDURE `sp_deleteOrderData`(orderid BIGINT(11))
BEGIN
DECLARE shipmentnumbers VARCHAR(1000);
DECLARE cartonid VARCHAR(1000);
SELECT GROUP_CONCAT(a_shipmentid) FROM t_shipment WHERE a_orderid = orderid INTO shipmentnumbers;
SELECT GROUP_CONCAT(a_cartonid) FROM t_carton WHERE a_shipmentid IN (shipmentnumbers) INTO cartonid;
SELECT shipmentnumbers;
/*SELECT cartonid; */
END$$
DELIMITER ;
Here shipmentnumbers returns 100020,100021,100022
Ideally cartonid should be returned as 11,12,13
But i get only 11 as cartonid.
But when i use below code i get proper result.
SELECT GROUP_CONCAT(a_cartonid) FROM t_carton WHERE FIND_IN_SET( a_shipmentid, shipmentnumbers ) INTO cartonid;
I wanted to know what exactly is the difference between IN and FIND_IN_SET and hwo di i decide what to use.

Answer 1

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.

Answer 2

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