POSTGRESQL交叉表的实现

浏览数：25 / 时间：2015年06月12日

这里我来演示下在POSTGRESQL里面如何实现交叉表的展示，至于什么是交叉表，我就不多说了，度娘去哦。
原始表数据如下：

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想要实现以下的结果：

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大致有以下几种方法：

1、用标准SQL展现出来

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2、用PostgreSQL 提供的第三方扩展 tablefunc 带来的函数实现
以下函数crosstab 里面的SQL必须有三个字段，name, 分类以及分类值来作为起始参数，必须以name,分类值作为输出参数。

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t_girl=# SELECT *
FROM crosstab(‘select name,subject,score from score order by name desc‘,$$values (‘English‘::text),(‘Physics‘::text),(‘Math‘::text)$$)
AS score(name text, English int, Physics int, Math int);
name | english | physics | math
-------+---------+---------+------
Simon | 90 | 76 | 79
Lucy | 100 | 90 | 85
Lily | 95 | 81 | 84
David | 100 | 86 | 89
(4 rows)
Time: 2.059 ms

3、用PostgreSQL 自身的聚合函数实现

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t_girl=# select name,split_part(split_part(tmp,‘,‘,1),‘:‘,2) as "English",
t_girl-# split_part(split_part(tmp,‘,‘,2),‘:‘,2) as "Physics",
t_girl-# split_part(split_part(tmp,‘,‘,3),‘:‘,2) as "Math"
t_girl-# from
t_girl-# (
t_girl(# select name,string_agg(subject||‘:‘||score,‘,‘) as tmp from score group by name order by name desc
t_girl(# ) as T;
name | English | Physics | Math
-------+---------+---------+------
Simon | 90 | 76 | 79
Lucy | 100 | 90 | 85
Lily | 95 | 81 | 84
David | 100 | 86 | 89
(4 rows)
Time: 2.396 ms

4、存储函数实现

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create or replace function func_ytt_crosstab_py ()
returns setof ytt_crosstab
as
$ytt$
for row in plpy.cursor("select name,string_agg(subject||‘:‘||score,‘,‘) as tmp from score group by name order by name desc"):
a = row[‘tmp‘].split(‘,‘)
yield (row[‘name‘],a[0].split(‘:‘)[1],a[1].split(‘:‘)[1],a[2].split(‘:‘)[1])
$ytt$ language plpythonu;
t_girl=# select name,english,physics,math from func_ytt_crosstab_py();
name | english | physics | math
-------+---------+---------+------
Simon | 90 | 76 | 79
Lucy | 100 | 90 | 85
Lily | 95 | 81 | 84
David | 100 | 86 | 89
(4 rows)
Time: 2.687 ms

5、用PLPGSQL来实现

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t_girl=# create type ytt_crosstab as (name text, English text, Physics text, Math text);
CREATE TYPE
Time: 22.518 ms
create or replace function func_ytt_crosstab ()
returns setof ytt_crosstab
as
$ytt$
declare v_name text := ‘‘;
v_english text := ‘‘;
v_physics text := ‘‘;
v_math text := ‘‘;
v_tmp_result text := ‘‘;
declare cs1 cursor for select name,string_agg(subject||‘:‘||score,‘,‘) from score group by name order by name desc;
begin
open cs1;
loop
fetch cs1 into v_name,v_tmp_result;
exit when not found;
v_english = split_part(split_part(v_tmp_result,‘,‘,1),‘:‘,2);
v_physics = split_part(split_part(v_tmp_result,‘,‘,2),‘:‘,2);
v_math = split_part(split_part(v_tmp_result,‘,‘,3),‘:‘,2);
return query select v_name,v_english,v_physics,v_math;
end loop;
end;
$ytt$ language plpgsql;
t_girl=# select name,English,Physics,Math from func_ytt_crosstab();
name | english | physics | math
-------+---------+---------+------
Simon | 90 | 76 | 79
Lucy | 100 | 90 | 85
Lily | 95 | 81 | 84
David | 100 | 86 | 89
(4 rows)
Time: 2.127 ms