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Re: Difference in columns

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Gurjeet Singh" <singh(dot)gurjeet(at)gmail(dot)com>
Cc: "Craig Ringer" <craig(at)postnewspapers(dot)com(dot)au>, "Mag Gam" <magawake(at)gmail(dot)com>, pgsql-sql(at)postgresql(dot)org
Subject: Re: Difference in columns
Date: 2008-05-11 18:58:02
Message-ID: 21842.1210532282@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-sql
"Gurjeet Singh" <singh(dot)gurjeet(at)gmail(dot)com> writes:
> On Sun, May 11, 2008 at 11:47 PM, Craig Ringer <craig(at)postnewspapers(dot)com(dot)au>
>> If you cannot assume that, you can use a subquery with limit and order
>> by to obtain the next record:
>> 
>> SELECT
>> a.ts,
>> (SELECT b.size FROM x b WHERE b.ts > a.ts ORDER BY b.ts ASC LIMIT 1)
>> - a.size AS difference
>> FROM x a;
>> 
>> ... but that'll be really slow for any significant number of entries.

> not really... if you have an index on the TS column.

The OP said this was a view, so it may well not have any easy way to
provide such an index.

			regards, tom lane

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