On Thu, 2004-08-19 at 17:21, Josh Berkus wrote:Jan,
> Because the value in b.y is redundant. b.x->a.x->a.y is exactly the same > value and he even wants to ensure this with the constraint.
And in the absence of that constraint, what ensures that b.y = a.y, exactly?
In the absence of b.y, it would be impossible for it to be anything else. Isn't that the point?
Precisely. I meant that the entire column is redundant and obsolete. Without the column, no need for any constraint.
It seems to me that he was trying to use the database to show errors in his source data, but since his constraint would reject the data, he wouldn't be able to enter it; all he could do would be to see the error. So he might as well turn it round, normalise the data properly and use the database to tell the rest of the system what the data ought to be.
I assumed he often queries b, and to avoid joining a all the time he duplicates values from a into b and then tries to ensure that they stay in sync with constraints.
Jan
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