SELECT JOIN MYSQL

Question

I have 2 tables which is user and userdata .

Once a customer buy a product, it will insert into table userdata and user .

In user table , the product id is recorded in user . buyid in form of "id, id ,id ,id ,id".

example : "23, 24". So I have tried to get all rows with id ( 23, 24 ) from product by using these queries

SELECT * FROM `userdata`,`user` WHERE `userdata`.`id` IN (`user`.`buyid`);

Query return 1 row product which is id=23

SELECT * FROM `user` INNER JOIN `userdata` ON `userdata`.`id` IN (`user`.`buyid`);

This too return only 1 row of product with id 23.

Expected result each row return this:

user.id | user.name | user.contact | product.id | product.name
1       | nazmi     | 99999        | 23         | A
1       | nazmi     | 99999        | 24         | B

Answer 1

Fix your data model! Storing lists of ids in a string is bad, bad, bad:

• Your id is an integer. It should be stored as a number, not a string.
• Your id refers to another table. It should have properly declared foreign key relationships.
• A column should contain a single column.
• SQL has a great way of storing lists. Really powerful. It is called a "table" not a "string column".
• String processing capabilities are pretty poor in SQL.
• Queries with such data structures cannot take advantage of indexes and partitioning.

Sometimes, you are stuck with other people's really, really, really bad decisions. MySQL offers a nice function (too nice in my opinion) to help:

SELECT *
FROM user u JOIN
     userdata ud
     ON find_in_set(ud.id, u.buyid) > 0;

If you have spaces in your id list, then you need to get rid of them. And the separator has to be a comma.

SELECT *
FROM user u JOIN
     userdata ud
     ON find_in_set(ud.id, replace(u.buyid, ' ', '')) > 0;