MySQL列和行条目删除

Question

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Ok so before I start let me state I am self taught and make alot of mistakes. I am also not very strong in sql query writing. Ok so I want to update this table by removing multiple membergroupids. I dont want anyone in membergroupids 2, 192, 10, 20. Ok as you can tell by the still visible commas I have worked a basic code to do one group at a time and it leaves the commas. I have over 120 membergroupids I need to clear from over 1800 rows. I also need to be able to put in another piece that I will worry about once I can get something done about this first.

Ok to review. Need to be able to remove above mentioned membergroupids from multiple rows in this table. If I need to explain it clearer please let me know as I am still trying to figure out all this SQL stuff.

 UPDATE user INNER JOIN userfield ON user.userid = userfield.userid SET `membergroupids` = replace(ltrim(rtrim(replace(concat(' ', replace(`membergroupids`, ',', ' '), ' '), ' 2 ', ' '))), ' ', ',') WHERE find_in_set('2', `membergroupids`) > 0 AND `field23` <= 0 AND (`membergroupids` LIKE '%' ',2,' '%' OR `membergroupids` LIKE '2,' '%' OR `membergroupids` LIKE '%' ',2' OR `membergroupids` LIKE '2'); 

That is the Code that myself and a friend came up with but it only does one membergroupids at a time.

Answer 1

Is membergroups a single field? And, in your table you have any number of records that may have the same membergroup and you're looking for a way to remove them all? That's how I understand it so correct me if I'm wrong.

I would use something like:

delete from table where membergroups in (2, 192, 10, 20)

It might not be possible, but ultimately it would be better to have your membergroupids in a separate table where one row represents each membergroupid each user belongs to. Then to remove them is a simple DELETE rather than a complicated SET update.

The query example you guys came up with is similar to what I'd do with your particular setup, but as you can see it can get messy after awhile.

On the other hand, if you can add membergroupids to a separate table setup like:

CREATE table user_groups(
userid  int,
membergroupid int);

Then you can remove membergroups quite simply.

Example 1: Remove member groups 2, 192, 10 and 20 for all users

delete from user_groups where membergroupid in (2, 192, 10, 20)

Example 2: Remove member groups 2, 192, 10 and 20 for users that are NOT members of groups 2 and 22.

delete from user_groups where membergroupid in (2, 192, 10, 20) and userid not in (select userid from user_groups where membergroupid in (2,22));

This setup, where we use a separate table instead of a field containing a set of values may seem like its less efficient, but it's not. Plus, you have much more flexibility when it comes to adding/removing membergroups and you don't have to deal with all the commas, concats, etc.