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Minor Description
When there are multiple constraints on a single table and the constraints have the same set of columns (in the same order), Derby tries to optimize things by re-using a single backing index for all of the relevant constraints. See the "executeConstantAction()" method of CreateIndexConstantAction.java (search for "duplicate").
But there is a bug in Derby where, if one of the constraints is unique and is dropped, the uniqueness "attribute" of the backing index is not updated accordingly. This means that uniqueness may be incorrectly enforced where it is not required.
Take the following example ("Case 2" from DERBY-2204):
ALTER TABLE NEWORDERS ADD CONSTRAINT
NEWORDERS_PK PRIMARY KEY(NO_W_ID, NO_D_ID, NO_O_ID);
ALTER TABLE NEWORDERS ADD CONSTRAINT
NO_O_FK FOREIGN KEY (NO_W_ID, NO_D_ID, NO_O_ID) REFERENCES ORDERS;
For these statements Derby will use a single backing index for both the primary constraint NEWORDERS_PK and the foreign key constraint NO_O_FK. That backing index will be unique because the primary key must itself be unique.
If later we drop the primary key:
ALTER TABLE NEWORDERS DROP CONSTRAINT NEWORDERS_PK;
then the backing index needs to be converted from a unique index to a non-unique index (because a foreign key is not inherently unique). But in Derby the uniqueness attribute remains unchanged, so attempts to insert a duplicate (NO_W_ID, NO_D_ID, NO_O_ID) row into NEWORDERS will fail with error 23505, when it should really succeed.
I tried this out on 10.1.3.1 and the same behavior occurs there, so marking "Affects" versions for everything back to that...
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Issue Links
- relates to
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DERBY-5249 A table created with 10.0.2.1 with constraints cannot be dropped with 10.5 due to NullPointerException with insane build or ASSERT FAILED Failed to find sharable conglomerate descriptor for index conglomerate with sane build
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- Closed
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