Suppose I have a table with 4 fields (f1, f2, f3, f4)
I define 2 unique indexes u1 (f1, f2, f3) and u2 (f1, f2, f4)
I have 3 records
A, B, C, D (this will be inserted)
A, B, C, E (this will pass u2, but not u1, thus not inserted)
A, B, F, D (this will pass u1, but not u2, thus not inserted)
Now, for performance ...
I have tables like this with 500.000 records where there's a new upload of approx. 20.000 records.
It is only now that we say index u2 to be necessary. So, until now, I did something like insert into ... select f1, f2, f2, max(f4) group by f1, f2, f3
That is ok ... and also logically ok because of the data definition
I cannot do this with 2 group by's. I tried this on paper and I'm not succeeding.
So, I must use a function that will check against u1 and u2, and then insert if it is ok.
I know that such a function is way slower that my insert query.
So, my question ...
How can I keep the same performance, but also with the new index in mind ???
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