PostgreSQL and pivot tables using crosstab function

问题

I have a problem with creating a pivot table in PostgreSQL using the crosstab() function. It works well but it produces multiple records for the same client_id. How can I avoid this?

Here is the SQL:

SELECT *
FROM crosstab('SELECT client_id
                     ,extract(year from date)
                     ,sum(amount)
               from   orders
               group  by extract(year from date)
                     ,client_id'
             ,'SELECT extract(year from date)
               FROM   orders
               GROUP  BY extract(year from date)
               order  by extract(year from date)')
AS orders(
row_name integer,
year_2001 text,
year_2002 text,
year_2003 text,
year_2004 text,
year_2005 text,
year_2006 text,
year_2007 text,
year_2008 text,
year_2009 text,
year_2010 text,
year_2011 text);

//Edit

Thx to Erwin it works now, but I have tried to do this without built in function with no luck. Can someone suggest something on that? My code for only two years:

SELECT DISTINCT o.client_id,
       CASE WHEN (extract(year from o.date)=2001)
            THEN sum(o.amount) ELSE 0 END,
       CASE WHEN (extract(year from o.date)=2002)
            THEN sum(o.amount) ELSE 0 END
FROM orders AS o
GROUP BY 1, extract(year from o.date)
ORDER BY 1;

回答1:

You need to ORDER BY the first query accordingly. I use the simplified syntax ORDER BY <ordinal number> here.

SELECT *
FROM   crosstab(
        'SELECT client_id
               ,extract(year from date)
               ,sum(amount)
         FROM   orders
         GROUP  BY 1,2
         ORDER  BY 1,2',

        'SELECT extract(year from date)
         FROM   orders
         GROUP  BY 1
         ORDER  BY 1')
AS orders(
    row_name integer,
    year_2001 text,
    year_2002 text,
    year_2003 text,
    year_2004 text,
    year_2005 text,
    year_2006 text,
    year_2007 text,
    year_2008 text,
    year_2009 text,
    year_2010 text,
    year_2011 text);

The crosstab() function is not included in standard PostgreSQL but comes with the additional module tablefunc.

Edit for additional request

Version without crosstab() function: Only group by client_id or you will end up with multiple rows per client_id.

SELECT client_id
      ,sum(CASE WHEN extract(year from date) = 2001 THEN amount ELSE 0 END) AS year_2001
      ,sum(CASE WHEN extract(year from date) = 2002 THEN amount ELSE 0 END) AS year_2002
       -- ...
FROM   orders o
GROUP  BY 1
ORDER  BY 1;

来源：https://stackoverflow.com/questions/8027293/postgresql-and-pivot-tables-using-crosstab-function

标签

sql

postgresql

pivot

crosstab