Implement POSTGRESQL cross tabulation

Implement POSTGRESQL cross tabulation
Here I will demonstrate how to implement cross-tabulation display in POSTGRESQL. As for what a cross-tabulation is, I will not talk much about it.
The raw table data is as follows:

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

To achieve the following results:

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

There are roughly the following methods:


1. Use standard SQL

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. Use a third-party extension provided by PostgreSQL to implement functions provided by tablefunc.
The SQL statement in crosstab must have three fields: name, category, and category value as the starting parameter. name and category value must be used as the output parameter.

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. Using PostgreSQL's own Aggregate functions

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-# 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. storage function implementation

create or replace function func_ytt_crosstab_py ()returns setof ytt_crosstabas $ytt$  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. Use PLPGSQL to implement

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,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