Re: complex column definition in query

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От A. Kretschmer
Тема Re: complex column definition in query
Дата
Msg-id 20090603050432.GA18756@a-kretschmer.de
обсуждение исходный текст
Ответ на complex column definition in query  (Seb <spluque@gmail.com>)
Список pgsql-sql
In response to Seb :
> Hi,
> 
> Say we have a table:
> 
> SELECT * FROM weather;
>      city      | temp_lo | temp_hi | prcp  
> ---------------+---------+---------+-------
>  San Francisco |      46 |      50 | 0.25 
>  San Francisco |      43 |      57 |    0 
>  Hayward       |      37 |      54 |      
>  Hayward       |      30 |      58 |      
>  Somewhere     |      25 |      60 |      
>  Somewhere     |      28 |      50 |      
> (6 rows)
> 
> I'm struggling to build a query with a column temp, where the first row
> is the lowest temp_lo followed by all the temp_hi for each city.  So
> this would be the output:
> 
>      city      | temp  
> ---------------+------
>  San Francisco |   43
>  San Francisco |   50 
>  San Francisco |   57 
>  Hayward       |   30
>  Hayward       |   54 
>  Hayward       |   58 
>  Somewhere     |   25
>  Somewhere     |   60 
>  Somewhere     |   50 
> (6 rows)
> 
> Any ideas appreciated!  Thanks.

test=# select * from weather ;    city      | temp_lo | temp_hi
---------------+---------+---------San Francisco |      46 |      50San Francisco |      43 |      57Hayward       |
 37 |      54Hayward       |      30 |      58
 
(4 rows)

test=*# select city, min(temp_lo) as temp from weather group by city union all select city, temp_hi from weather order
by1,2;    city      | temp
 
---------------+------Hayward       |   30Hayward       |   54Hayward       |   58San Francisco |   43San Francisco |
50SanFrancisco |   57
 
(6 rows)



HTH, Andreas
-- 
Andreas Kretschmer
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