Hi,
Constraints seem to be checked before making the change which is wrong.
Test case:
-- Create table with one boolean column
CREATE TABLE T1 ( A BOOLEAN NOT NULL );
-- Add a constraint that ensures that the table can contain at most 2
TRUE values
ALTER TABLE T1 ADD CONSTRAINT C1 CHECK (
( SELECT SUM(CAST(A AS INT)) FROM T1) < 3
);
-- Insert 3 TRUE values in single pass. Should give an error but does not
INSERT INTO T1 VALUES (TRUE), (TRUE), (TRUE)
-- Now inserting false which never should fail gives an error because
the table is in inconsistent state
INSERT INTO T1 VALUES (FALSE)
The same problem occurs when inserting the true values one by one.
The third succeeds making the check constraint always fail before
deleting at least one true value.
So deducing from this behaviour it seems that the constraint check is
done before the changes which of course makes no sense.
- Rami
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