[EMAIL PROTECTED] wrote:
Hello,
I've got 2 tables, "url" (U), and "bookmark" (B), with "bookmark" pointing to
"url" via FK.
Somehow I ended up with some rows in B referencing non-existent rows in U.
This sounds super strange and dangerous to me, and it's not clear to me how/why
PG let this happen.
I'm using 8.0.3.
Here are the table references I just mentioned:
Table "bookmark":
id SERIAL
CONSTRAINT pk_bookmark_id PRIMARY KEY
Table "url":
url_id INTEGER
CONSTRAINT fk_bookmark_id REFERENCES bookmark(id)
Your DDL doesn't say : "B references U", but the contrary : "U
references B".
So it's perfectly right that somes tuples in B are not referenced by
tuples in U.
Please correct your constraints.
Problem #1: Strange that PG allowed this to happen. Maybe my DDL above allows
this to happen and needs to be tightened? I thought the above would ensure
referential integrity, but maybe I need to specify something else?
Problem #2: I'd like to find all rows in B that point to non-existent rows in
U. I can do it with the following sub-select, I believe, but it's rather
inefficient (EXPLAIN shows both tables would be sequentially scanned):
SELECT * FROM bookmark WHERE id NOT IN (SELECT b.id FROM bookmark b, url u
WHERE b.url_id=u.id);
Is there a more efficient way to get the rows from "bookmark"?
Thanks,
Otis
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TIP 6: explain analyze is your friend
I think, for that one Scott's answer is OK
You could also try SELECT * FROM url U WHERE NOT EXISTS(SELECT * FROM
bookmark B WHERE B.url-id=U.id)
and see wich one is faster
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TIP 2: Don't 'kill -9' the postmaster
