No, they shouldn't. If you want to delete only those tuples that aren't referenced in b then you must explicitly say so:
delete from a where not exists (select * from b where b.b = a.a);
The query that you tried will explicitly delete all rows from a, thus violating the constraint on b. If even one row fails, then the transaction fails, rolling back any other deletes that may have been successful.
Cheers...
MikeA
>> -----Original Message-----
>> From: Gavin Sherry [mailto:[EMAIL PROTECTED]]
>> Sent: 17 April 2001 09:59
>> To: [EMAIL PROTECTED]
>> Subject: [HACKERS] Foreign key checks/referential integrity.
>>
>>
>> Hi guys,
>>
>> I've just come up with a hypothetical which, in my opinion,
>> points to a
>> flaw in the foreign key implementation in Postgres. All tests were
>> conducted on 7.1beta4 -- not the most up to date, but I have seen no
>> reference to this in the mailing list/todo (ie, in 'foreign' under
>> TODO.detail).
>>
>> See as follows:
>>
>> test=# create table a (a int, primary key(a));
>> NOTICE: CREATE TABLE/PRIMARY KEY will create implicit index
>> 'a_pkey' for
>> table
>> 'a'
>> CREATE
>> test=# create table b (b int references a(a) match full,
>> primary key(b));
>> NOTICE: CREATE TABLE/PRIMARY KEY will create implicit index
>> 'b_pkey' for
>> table
>> 'b'
>> NOTICE: CREATE TABLE will create implicit trigger(s) for FOREIGN KEY
>> check(s)
>> CREATE
>> test=# insert into a values(1);
>> INSERT 1754732 1
>> test=# insert into a values(2);
>> INSERT 1754733 1
>> test=# insert into a values(3);
>> INSERT 1754734 1
>> test=# insert into b values(1);
>> INSERT 1754735 1
>> test=# insert into b values(2);
>> INSERT 1754736 1
>> test=# delete from a;
>> ERROR: <unnamed> referential integrity violation - key in a still
>> referenced from b
>> test=# select * from a;
>> a
>> ---
>> 1
>> 2
>> 3
>>
>>
>> ----
>>
>> Now, table a has more tuples than b. In my opinion, the
>> integrity test
>> relates only to those records in a which are in b (since it
>> is a foreign
>> key reference). Isn't then the query valid for those tuples
>> which do not
>> result in a violation of the referential integrity test?
>> Shouldn't those
>> tuples in a be deleted?
>>
>> Gavin
>>
>>
>>
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