PostgreSQL的行转列函数使用一例

开发同事说使用postgres的扩展行转列应用时有一个问题，示例如下 该扩展包初步使用参考： http://my.oschina.net/Kenyon/blog/54357 一、环境 OS:

开发同事说使用postgres的扩展行转列应用时有一个问题，示例如下

该扩展包初步使用参考： http://my.oschina.net/Kenyon/blog/54357

一、环境
OS:CentOS 6.3
DB:PostgreSQL 9.3.0

二、场景

create table t(day date,equipment varchar(20),output integer);insert into t values('2010-04-01','DAT501',100);insert into t values('2010-04-01','DAT502',120);insert into t values('2010-04-01','DAT503',130);insert into t values('2010-04-02','DAT501',110);insert into t values('2010-04-02','DAT502',105); insert into t values('2010-04-03','DAT503',125);insert into t values('2010-04-04','DAT501',100);insert into t values('2010-04-04','DAT503',200);--想得到如下结果    day     | dat501 | dat502 | dat503 ------------+--------+--------+-------- 2010-04-01 |    100 |    120 |    130 2010-04-02 |    110 |    105 |        2010-04-03 |        |        |    125 2010-04-04 |    100 |        |    200     (4 rows)--但是直接使用crosstab会导致第3,4行不准确，也就是说中间项为Null就会不准test=# SELECT * FROM crosstab('select day, equipment, output from t order by 1,2')  AS t(day date, DAT501 integer, DAT502 integer,DAT503 integer);    day     | dat501 | dat502 | dat503 ------------+--------+--------+-------- 2010-04-01 |    100 |    120 |    130 2010-04-02 |    110 |    105 |        2010-04-03 |    125 |        |        2010-04-04 |    100 |    200 |       (4 rows)

三、解决
crosstab还有一个包含两个输入参数的用法，用这个可以解决上述问题

test=# SELECT * FROM crosstab('select day, equipment, output from t order by 1,2',$$values('DAT501'::text),('DAT502'::text),('DAT503'::text)$$)  AS t(day date, DAT501 integer, DAT502 integer,DAT503 integer);    day     | dat501 | dat502 | dat503 ------------+--------+--------+-------- 2010-04-01 |    100 |    120 |    130 2010-04-02 |    110 |    105 |        2010-04-03 |        |        |    125 2010-04-04 |    100 |        |    200(4 rows)

--其他的写法,本质都一样

test=# SELECT * FROM crosstab('select day, equipment, output from t order by 1','select distinct equipment  from t order by 1')  AS t(day date, DAT501 integer, DAT502 integer,DAT503 integer);    day     | dat501 | dat502 | dat503 ------------+--------+--------+-------- 2010-04-01 |    100 |    120 |    130 2010-04-02 |    110 |    105 |        2010-04-03 |        |        |    125 2010-04-04 |    100 |        |    200(4 rows)

四、说明
使用两个参数的crosstab其实更安全，推荐使用，其基础用法是

crosstab(text source_sql, text category_sql)

 
参考：
http://www.postgresql.org/docs/9.2/static/tablefunc.html