Обсуждение: stupid select question...

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 something
like this with a
select url from table1 where a.url not in select url from table b.

Can I do this in postgres?

Konstantin
--
Dipl-Inf. Konstantin Agouros aka Elwood Blues. Internet: elwood@agouros.de
Otkerstr. 28, 81547 Muenchen, Germany. Tel +49 89 69370185
----------------------------------------------------------------------------
"Captain, this ship will not sustain the forming of the cosmos." B'Elana Torres

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)

--
Oliver Elphick                                Oliver.Elphick@lfix.co.uk
Isle of Wight                              http://www.lfix.co.uk/oliver
PGP: 1024R/32B8FAA1: 97 EA 1D 47 72 3F 28 47  6B 7E 39 CC 56 E4 C1 47
GPG: 1024D/3E1D0C1C: CA12 09E0 E8D5 8870 5839  932A 614D 4C34 3E1D 0C1C
                 ========================================
     "If we confess our sins, he is faithful and just to
      forgive us our sins, and to cleanse us from all
      unrighteousness."          I John 1:9

NOT IN will not work if u have nulls in the list.
Anand
On Sun, Jan 14, 2001 at 01:25:59PM +0000, Oliver Elphick wrote:
>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)
>
>--
>Oliver Elphick                                Oliver.Elphick@lfix.co.uk
>Isle of Wight                              http://www.lfix.co.uk/oliver
>PGP: 1024R/32B8FAA1: 97 EA 1D 47 72 3F 28 47  6B 7E 39 CC 56 E4 C1 47
>GPG: 1024D/3E1D0C1C: CA12 09E0 E8D5 8870 5839  932A 614D 4C34 3E1D 0C1C
>                 ========================================
>     "If we confess our sins, he is faithful and just to
>      forgive us our sins, and to cleanse us from all
>      unrighteousness."          I John 1:9
>