How to transpose columns and rows in PostgreSQL (i

问题:

Possible Duplicate:
Transposing an sql result so that one column goes onto multiple columns

I'd like to do a sort of row/column swapping in my PSQL database. Here's my example database:

id  place   price   year
1   U.S.    80  2000
2   U.S.    60  2001
3   U.S.    40  2002    
4   U.K.    600 2000
5   U.K.    500 2001
6   U.K.    350 2002

I would like to transform that table into the following example:

year    U.S.    U.K.
2000    80  600
2001    60  500
2002    40  350

Is this possible in PostgreSQL?

回答1:

You can do this easily with an aggregate function and a CASE statement:

select year,
  sum(case when place = 'U.S.' then price else 0 end) "U.S.",
  sum(case when place = 'U.K.' then price else 0 end) "U.K."
from yourtable
group by year

See SQL Fiddle with Demo

回答2:

This is called a "pivot", and there's no special syntax in postgres to support it - you have to code it using SQL, for example:

select
    year,
    us.price as us,
    uk.price as uk
from mytable us
left join mytable uk on us.year = uk.year