database implementation constraints and documentation

Question

a constraint requires me that. "the value of B, present in table B1, must always be less than that of A present in table C1".

is it correct to implement two triggers to do this? one that is activated when B1 is inserted and modified and one when C1 is modified?

In the constraint dictionary documentation should it be indicated with a single constraint or separate ones?

Or... you can add redundancy to table B1 and use a trivial constraint there. — The Impaler
– The Impaler, Commented May 15 at 18:01

Christophe · Accepted Answer · 2025-05-18 13:59:43Z

0

The constraint spans two tables. So you cannot consider constraint checks as these are limited to a simple expression involving only columns of the same table.

Since each table could be updated independently, it is correct to consider a solution based on two BEFORE triggers, an UPDATE trigger on C1 and an UPDATE/INSERT trigger on B1 .

Regarding documentation, it is conceptually a single constraint in the model, which has to be enforced in two places in the implementation. I'd therefore recommend to document it as one constraint that is cross referenced several time in the implementation. This allows to keep the picture and remind that it is the two sides of the same coin, and not two different constraints. (unless you refer to some dictionary in a supporting tool, in which case you'd need to say more)

answered May 18 at 13:59

Christophe

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