Create a pivot table with PostgreSQL

问题

Suppose I have a table in Postgres called listings that looks like this:

id    neighborhood    bedrooms    price
1     downtown        0           256888
2     downtown        1           334000
3     riverview       1           505000
etc.

How do I write a crosstab query that shows the average price per bedrooms as the columns and neighborhoods as the rows?

The output of the query should look something like this (numbers are made up, columns are the bedrooms):

            0       1       2       3
riverton    250000  300000  350000  -
downtown    189000  325000  -       450000

回答1:

First compute the average with the aggregate function avg():

SELECT neighborhood, bedrooms, avg(price)
FROM   listings
GROUP  BY 1,2
ORDER  BY 1,2

Then feed the result to the crosstab() function as instructed in great detail in this related answer:

PostgreSQL Crosstab Query

回答2:

The best way to build pivot tables in Postgres is Case statements.

select neighborhood,
round(avg((case when bedroom = 0 then price else 0 end)),2) as "0",
round(avg((case when bedroom = 1 then price else 0 end)),2) as "1",
round(avg((case when bedroom = 2 then price else 0 end)),2) as "2",
round(avg((case when bedroom = 3 then price else 0 end)),2) as "3",
from listings
group by neighborhood;

This was my output

NEIGHBORHOOD                  0          1          2          3
-------------------- ---------- ---------- ---------- ----------
downtown                      0     373.38     328.25     524.63
riverview                     0     256.83          0       1341
north                         0     199.15     507.85     986.31

来源：https://stackoverflow.com/questions/20618323/create-a-pivot-table-with-postgresql

标签

sql

database

postgresql

aggregate-functions

crosstab