PostgreSQL实现交叉表（行列转换）的5种方法示例

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 

name | English | Physics | Math 
------+---------+---------+------ 
Simon |  90 |  76 | 79 
Lucy |  100 |  90 | 85 
Lily |  95 |  81 | 84 
David |  100 |  86 | 89 

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 

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 

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 

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 

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