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ghost-in-the-zsh provided a direct answer and I will try to offer a more general complementary one. One possible thing to try is a trigger that checks the integrity, but it cannot work for insert...
Answer
#1: Initial revision
by
Alexei
·
2020-11-10T21:30:31Z (over 3 years ago)
`ghost-in-the-zsh` provided a direct answer and I will try to offer a more general complementary one.
One possible thing to try is a trigger that checks the integrity, but it cannot work for inserts because the order must be something along the lines:
START TRANSACTION
INSERT INTO B
INSERT INTO A
INSERT INTO AxB
COMMIT
Since A's records must be checked, a trigger for A would make sense, but it would fire too early. A trigger on AxB would not prevent simple changes in A that do not connect to any B record.
For more complex validations one way is to ensure then from the application layer since it seems that the data is always changed by it. Integrity is ensured by **the proper use of transactions** and automatic testing.
As a safety net, a job might periodically check this integrity (this technique is used the data volume is big enough to make constraints checking quite expensive).