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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Oliver Elphick Oliver.Elphick@lfix.co.uk
Isle of Wight http://www.lfix.co.uk/oliver
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unrighteousness." I John 1:9

NOT IN will not work if u have nulls in the list.
Anand