Re: stupid select question...

Konstantinos Agouros wrote:
>
>Hi,
>
>my sql has gotten a little rusty, here's what I want to do:
>I have two tables both contain urls. How what I want are all the entries in
>table b where there is no matching url in table a. I do remember doing somet
>hing
>like this with a
>select url from table1 where a.url not in select url from table b.
>
>Can I do this in postgres?

SELECT url FROM a WHERE url NOT IN (select url FROM b);

but watch out for nulls:

bray=# select * from a;
url
------------
http:fred1
http:fred2
(2 rows)

bray=# select * from b;
id | url
----+------------
1 | http:fred1
2 | <-- url is null
(2 rows)

bray=# SELECT url FROM a WHERE url NOT IN (select url FROM b);
url
-----
(0 rows)

bray=# SELECT url FROM a WHERE url NOT IN (select url FROM b WHERE NOT url IS
NULL);
url
------------
http:fred2
(1 row)

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