POSTGRESQL交叉表的实现

概述这里我来演示下在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 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 scoret_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 ms

3、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",3),2) as "Math"t_girl-# fromt_girl-# (t_girl(# select name,string_agg(subject||':'||score,') as tmp from score group by name order by name desct_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_crosstabas $ytt$  for row in plpy.cursor("select name,') 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

t_girl=# create type ytt_crosstab as (name text,English text,Physics text,Math text);CREATE TYPETime: 22.518 mscreate or replace function func_ytt_crosstab ()returns setof ytt_crosstabas $ytt$  declare v_name text := '';                v_english text := '';		v_physics text := '';		v_math text := '';		v_tmp_result text := '';  declare cs1 cursor for select name,') 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,2);    v_physics = split_part(split_part(v_tmp_result,2);    v_math = split_part(split_part(v_tmp_result,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

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