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： t_girl=#select*fromscore;name|subject|score-------+---------+-------Lucy|English|100Lucy|Physics|90Lucy|Math|85Lily|English|95L
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：
t_girl=# select * from score; name | subject | score -------+---------+------- Lucy | English | 100 Lucy | Physics | 90 Lucy | Math | 85 Lily | English | 95 Lily | Physics | 81 Lily | Math | 84 David | English | 100 David | Physics | 86 David | Math | 89 Simon | English | 90 Simon | Physics | 76 Simon | Math | 79 (12 rows) Time: 2.066 ms
想要实现以下的结果：
name | English | Physics | Math -------+---------+---------+------ Simon | 90 | 76 | 79 Lucy | 100 | 90 | 85 Lily | 95 | 81 | 84 David | 100 | 86 | 89
大致有以下几种方法：
1、用标准SQL展现出来
t_girl=# select name, t_girl-# sum(case when subject = 'English' then score else 0 end) as "English", t_girl-# sum(case when subject = 'Physics' then score else 0 end) as "Physics", t_girl-# sum(case when subject = 'Math' then score else 0 end) as "Math" t_girl-# from score t_girl-# group by name order by name desc; name | English | Physics | Math -------+---------+---------+------ Simon | 90 | 76 | 79 Lucy | 100 | 90 | 85 Lily | 95 | 81 | 84 David | 100 | 86 | 89 (4 rows) Time: 1.123 ms
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。
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 ms3、用PostgreSQL 自身的聚合函数实现
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
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 ms5、 用PLPGSQL来实现
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
