Re: which Update quicker - Mailing list pgsql-general

From Daniele Varrazzo
Subject Re: which Update quicker
Date
Msg-id CA+mi_8a3HqWZnGyjoxDV=RfvvapPdu44nCH06bGW+C9n967XQQ@mail.gmail.com
Whole thread Raw
In response to which Update quicker  (Emi Lu <emilu@encs.concordia.ca>)
List pgsql-general
On Tue, Sep 23, 2014 at 8:35 PM, Emi Lu <emilu@encs.concordia.ca> wrote:
> Hello list,
>
> For a big table with more than 1,000,000 records, may I know which update is
> quicker please?
>
> (1) update t1
>       set c1 = a.c1
>       from a
>       where pk and
>                  t1.c1       <> a.c1;
>  ......
>       update t1
>       set c_N = a.c_N
>       from a
>       where pk and
>                  t1.c_N       <> a.c_N;
>
>
> (2)  update t1
>       set c1 = a.c1 ,
>             c2  = a.c2,
>             ...
>             c_N = a.c_N
>      from a
>      where pk AND
>                (  t1.c1 <> a.c1 OR t1.c2 <> a.c2..... t1.c_N <> a.c_N)

Definitely the second, and it produces less bloat too.


> Or other quicker way for update action?

You may express the comparison as (t1.c1, t1.c2, ... t1.cN) <> (t2.c1,
t2.c2, ... t2.cN)
It's not going to be faster but maybe it's more readable.


-- Daniele


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