Message-ID: <4CBFF55D.1060200@archonet.com>
Date: Thu, 21 Oct 2010 09:10:05 +0100
From: Richard Huxton <dev@archonet.com>
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To: Nicholas I <nicholas.domnic.i@gmail.com>
CC: pgsql-sql@postgresql.org
Subject: Re: Need help on update.
References: <AANLkTi=nyWz=SNYZ+uLNPeUKOTgSscVqZR6CRTUkL99z@mail.gmail.com>
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On 21/10/10 08:43, Nicholas I wrote:
> Hi,
>
> there are two tables, table1 and table2, each having same column name
> called sn_no,name. i want to update table1 names with table2 where sn_no
> are same.
>
> select * from table1;
> sn_no |   name
> -------+-----------
>       1 | ramnad
>       2 | bangalore
>       3 | chennai
>
>
> select * from table2;
>   sn_no |   name
> -------+-----------
>       1 | Hyderabad
>       2 | Delhi
>       3 | Bombay
>
> Any help ?
>
> I tried with , some of the queries like,

Close. This is surprisingly difficult in standard SQL. PostgreSQL has a 
(non-standard) FROM clause you can use though.

BEGIN;

CREATE TABLE table1 (sn int, nm text);
CREATE TABLE table2 (sn int, nm text);
INSERT INTO table1 VALUES (1,'ramnad'),(2,'bangalore'),(3,'chennai');
INSERT INTO table2 VALUES (1,'Hyderabad'),(2,'Delhi'),(3,'Bombay');

UPDATE table1 SET nm = table2.nm
FROM table2
WHERE table1.sn = table2.sn;

SELECT * FROM table1;

ROLLBACK;

Be careful with aliasing the target of the update (table1 in this case). 
As another poster has discovered, that counts as another table in your join.

-- 
   Richard Huxton
   Archonet Ltd