Re: ORDER BY - Mailing list pgsql-general

From John Sidney-Woollett
Subject Re: ORDER BY
Date
Msg-id 455C089C.50202@wardbrook.com
Whole thread Raw
In response to Re: ORDER BY  ("George Pavlov" <gpavlov@mynewplace.com>)
List pgsql-general
Alternative options for what they're worth - you'd have to explain to
see how efficient they are

select id, name from (
   select lower(name) as sortkey, id, name from table where name != 'Other'
   union
   select 'zzzzz' as sortkey, id, name from table where name = 'Other'
) as t
order by sortkey


select id, name from (
   select case when name='Other' then 'zzzzz' else lower(name) end as
sortkey, id, name from table

) as t
order by sortkey

Notice that the sort will be case insensitive in these examples which
may be something that you also want.

John

George Pavlov wrote:
>> For larger tables, you may have to resort to a
>> union:
>>
>>    select * from foo where name != 'Other' order by name
>>    union
>>    select * from foo where name = 'Other'
>
> Alas, this suggestion is wrong on two counts: (a) UNION expects a single
> ORDER BY that applies to the whole recordset and which has to come at
> the end; (b) UNION re-sorts anyway (it needs to eliminate the dupes) --
> maybe you are thinking UNION ALL? So, to follow your advice he may want
> a query like this, although it seems quite silly and there still isn't
> an ironclad guarantee re. the final result sorting:
>
> select * from
>   (select * from foo where name != 'Other' order by name) x
> union all
> select * from foo where name = 'Other'
>
> ---------------------------(end of broadcast)---------------------------
> TIP 9: In versions below 8.0, the planner will ignore your desire to
>        choose an index scan if your joining column's datatypes do not
>        match

pgsql-general by date:

Previous
From: Tom Lane
Date:
Subject: Re: schema rename - is analyze necessary?
Next
From: Tom Lane
Date:
Subject: Re: Recovering deleted or updated rows