MySQL comma-separated string how to correctly delete

There is a field arrchildid value of 21,11,1,2
I want to delete 1 of them and run MySQL

UPDATE ' category ' SET ' Arrchildid ' =replace (' arrchildid ', ', 1 ', ') WHERE ' catid ' =100

Results should not be deleted also deleted, there is any good solution, thank you very much
Phpcms used this data structure, but I didn't find out how he handled it. When a category is deleted or modified, the Arrchildid field of its parent category is definitely to be changed.

Reply to discussion (solution)

UPDATE ' category ' SET ' Arrchildid ' =replace (concat (' Arrchildid ', ', '), ', 1, ', ') WHERE ' catid ' =100

There is a field arrchildid value of 21,11,1,2
I want to delete 1 of them and run MySQL

UPDATE ' category ' SET ' Arrchildid ' =replace (' arrchildid ', ', 1 ', ') WHERE ' catid ' =100

Results should not be deleted also deleted, there is any good solution, thank you very much
Phpcms used this data structure, but I didn't find out how he handled it. When a category is deleted or modified, the Arrchildid field of its parent category is definitely to be changed.

I ran the statement in phpMyAdmin and there was a better workaround if the Arrchildid value was 21,2,11,1 and could not be replaced.

There is a field arrchildid value of 21,11,1,2
I want to delete 1 of them and run MySQL

UPDATE ' category ' SET ' Arrchildid ' =replace (' arrchildid ', ', 1 ', ') WHERE ' catid ' =100

Results should not be deleted also deleted, there is any good solution, thank you very much
Phpcms used this data structure, but I didn't find out how he handled it. When a category is deleted or modified, the Arrchildid field of its parent category is definitely to be changed.

I ran the statement in phpMyAdmin and there was a better workaround if the Arrchildid value was 21,2,11,1 and could not be replaced.

Do not know what is the reason, manually hit the SQL will not be wrong

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