How to duplicate a row in mysql?

Question

MySQL

Hello. The situation is as follows, there is a table with records, there is a field in which there can be either one or several values ​​separated by commas (Group1, group2, group3, etc.).
How can I make a record where several values ​​are cloned by the number of these values, that is, a record for Group1, a record for Group2, etc.

Answer 1

You can do it, but most likely you have problems with the data model. If such a task arises, then the groups are placed in a separate table and a connection is made with the original table.
If you need it with such a model, then here is the request:

SELECT id, SUBSTRING_INDEX(SUBSTRING_INDEX(groups, ',', g.n), ',', -1) groupName
FROM (
    SELECT @n:[email protected]+1 n FROM 
      (select 0 union all select 1 union all select 3 union all select 4 union all select 5 union all select 6 union all select 6 union all select 7 union all select 8 union all select 9) s0,
      (select 0 union all select 1 union all select 3 union all select 4 union all select 5 union all select 6 union all select 6 union all select 7 union all select 8 union all select 9) s1,
      (SELECT @n:=0) sg
    ) g
    JOIN Item ON CHAR_LENGTH(groups)-CHAR_LENGTH(REPLACE(groups, ',', '')) >= g.n-1
ORDER BY id, n

Here is a link to a working example on sqlfiddle . This example assumes that each entry has no more than 100 groups. If they are always less than 10, then table s1 can be removed from the query.