Dynamic pivot query using PostgreSQL 9.3

问题

I have a table named as Product:

create table product (
    ProductNumber varchar(10),
    ProductName varchar(10),
    SalesQuantity int,
    Salescountry varchar(10)
);  

Sample values:

insert into product values
  ('P1', 'PenDrive', 50,  'US')
, ('P2', 'Mouse',    100, 'UK')
, ('P3', 'KeyBoard', 250, 'US')
, ('P1', 'PenDrive', 300, 'US')
, ('P2', 'Mouse',    450, 'UK')
, ('P5', 'Dvd',      50,  'UAE');   

I want to generate the Salescountry's names dynamically and show the sum of SalesQuantity sale in that Country.

Expected result:

ProductName US    UK    UAE
----------------------------
PenDrive    350   0     0
Mouse       0     550   0
KeyBoard    250   0     0
Dvd         0     0     50

I did it using SQL Server 2008 R2:

DECLARE @cols AS NVARCHAR(MAX),
        @query  AS NVARCHAR(MAX);

SET @cols = STUFF((SELECT distinct ',' + QUOTENAME(SalesCountry) 
            FROM Product
            FOR XML PATH(''), TYPE
            ).value('.', 'NVARCHAR(MAX)') 
        ,1,1,'')

set @query = 'SELECT ProductName, ' + @cols + ' from 
            (
                select ProductName
                    , SalesQuantity as q
                    , Salescountry
                from Product
           ) x
            pivot 
            (
                 SUM(q)
                for Salescountry in (' + @cols + ')
            ) p '

PRINT(@query);
execute(@query);

How to achieve this in Postgres?

回答1:

SELECT *
FROM   crosstab (
   'SELECT ProductNumber, ProductName, Salescountry, SalesQuantity
    FROM   product
    ORDER  BY 1'
, $$SELECT unnest('{US,UK,UAE1}'::varchar[])$$
  ) AS ct (
   "ProductNumber" varchar
 , "ProductName"   varchar
 , "US"   int
 , "UK"   int
 , "UAE1" int);

Detailed explanation:

• PostgreSQL Crosstab Query
• Pivot on Multiple Columns using Tablefunc

Completely dynamic query for varying number of distinct Salescountry?

• Dynamic alternative to pivot with CASE and GROUP BY

回答2:

While it's a two step process, this method will create a pivot with dynamic columns, without the need to specify the result set and without creating temp tables.

First we define a function that creates a dynamically prepared statement:

CREATE OR REPLACE FUNCTION flowms.pivotcode_sql(
    tablename character varying,
    rowc character varying,
    colc character varying,
    cellc character varying,
    celldatatype character varying)
    RETURNS character varying
    LANGUAGE 'plpgsql'

    COST 100
    VOLATILE 
AS $BODY$

declare
    dynsql1 varchar;
    dynsql2 varchar;
    columnlist varchar;
begin
    -- 1. retrieve list of column names.
    dynsql1 = 'select string_agg(distinct ''"''||'||colc||'||''" '||celldatatype||''','','' order by ''"''||'||colc||'||''" '||celldatatype||''') from '||tablename||';';
    execute dynsql1 into columnlist;
    -- 2. set up the crosstab query
    --tablename = REPLACE(text, ''', E'\\"')
    dynsql2 = 'prepare crosstab_stmt as select * from crosstab (
 ''select '||rowc||','||colc||','||cellc||' from '||replace(tablename, chr(39),E'\'\'')||' group by 1,2 order by 1,2'',
 ''select distinct '||colc||' from '||replace(tablename, chr(39),E'\'\'')||' order by 1''
 )
 as newtable (
 '||rowc||' varchar,'||columnlist||'
 );';
    deallocate all;
    execute dynsql2;
    return dynsql2;
end

$BODY$;

You can now call the function

select pivotcode_sql('tablename', 'rowfield', 'columnfield', 'sum(value)', 'integer');

which will create the prepared statement. Next you can execute the prepared statement:

execute crosstab_stmt;

来源：https://stackoverflow.com/questions/28087948/dynamic-pivot-query-using-postgresql-9-3