Optimize creation of UNIQUE constraints which can be determined to be already
Unique based on other constraints.
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Key: CORE-4956
URL: http://tracker.firebirdsql.org/browse/CORE-4956
Project: Firebird Core
Issue Type: Improvement
Affects Versions: 3.0 Beta 2
Reporter: Tim Kelly
Optimization request:
I have a large database and regularly have to create/modify UNIQUE constraints.
Most of my unique constraints contain two fields where the first field is
already the primary key, I create them to allow foreign keys to point to them.
I notice that is can sometimes take a long time to create the unique
constraint. Presumably a check is being performed that the existing data will
not violate the unique constraint. If so this step should not be required if it
can be determined that the UNIQUE constraint will already be unique by
definition. In my case:
ALTER TABLE MASTER ADD CONSTRAINT C UNIQUE (A,B);
Where A is the primary key of MASTER. We know 100% that the existing data will
not violate this constraint.
Since A is already known to be a primary key then it should not be necessary to
check the data before creating the constraint.
If I then created another constraint D:
ALTER TABLE MASTER ADD CONSTRAINT D UNIQUE (A,B,C);
Again no checks should need to be carried out as we already know that A,B is
unique so A,B,C will always be unique too.
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