Message-ID: <4F96EC90.6070600@encs.concordia.ca>
Date: Tue, 24 Apr 2012 14:10:24 -0400
From: Emi Lu <emilu@encs.concordia.ca>
Reply-To: emilu@encs.concordia.ca
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To: Steve Crawford <scrawford@pinpointresearch.com>
CC: pgsql-sql@postgresql.org,
	"pgsql-general@postgresql.org >> \"pgsql-general@postgresql.org\""
	<pgsql-general@postgresql.org>
Subject: Re: [SQL] Simple way to get missing number
References: <4F96B57E.8080306@encs.concordia.ca>
	<4F96C9E9.7000005@pinpointresearch.com>
In-Reply-To: <4F96C9E9.7000005@pinpointresearch.com>
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I got it and thank you very much for everyone's help!!

It seems that "left join where is null" is faster comparing with 
"except". And my final query is:

select num as missing
from   generate_series(5000, #{max_id}) t(num)
left join t1  on (t.num = t1.id)
where t1.id is null;

Emi

On 04/24/2012 11:42 AM, Steve Crawford wrote:
> On 04/24/2012 07:15 AM, Emi Lu wrote:
>> Good morning,
>>
>> May I know is there a simple sql command which could return missing
>> numbers please?
>>
>> For example,
>>
>> t1(id integer)
>>
>> values= 1, 2, 3 .... 5000000
>>
>> select miss_num(id)
>> from t1 ;
>>
>>
>> Will return:
>> ===============
>> 37, 800, 8001
>>
>> T
>
> select generate_series(1,5000000) except select id from t1;
>
> Example
>
> select anumber from fooo;
> anumber
> ---------
> 1
> 3
> 5
> 7
> 9
> 11
> 13
> 15
>
> select generate_series(1,15) except select anumber from fooo order by 1;
> generate_series
> -----------------
> 2
> 4
> 6
> 8
> 10
> 12
> 14
>
> Cheers,
> Steve