Postgres 14

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.
create table Subject (
 id serial primary key, 
 name varchar(30) not null
 );

insert into Subject (id, name) values
 (1 ,'fruit')
,(2 ,'drink')
,(3 ,'vege')
,(4 ,'fish');
 
create table Journal (
 id int, 
 subj int, 
 reference varchar(30), 
 value int
);

insert into Journal   
(id, subj, reference, value) values
 (1, 1, 'foo', 30)
,(2, 2, 'bar', 20)
,(3, 1, 'bar', 35)
,(4, 1, 'bar' ,10)
,(5, 2, 'baz', 25)
,(6, 4, 'foo', 30)
,(7, 4, 'bar', 40)
,(8, 1, 'baz', 20)
,(9, 2, 'bar', 5);

CREATE TABLE



INSERT 0 4



CREATE TABLE



INSERT 0 9


SELECT $f$SELECT * FROM crosstab(
     $$SELECT DISTINCT ON (1, 2)
       j.reference, 'subj_'||j.subj||'_'||s.name AS data_type, SUM(j.value) AS val
       FROM Journal j
       JOIN Subject s ON s.id = j.subj
       GROUP BY j.reference, j.subj, s.name
       ORDER BY j.reference$$

    ,$$VALUES ($f$     || string_agg(quote_literal(data_type), '), (') || $f$)$$)
AS x (reference text, $f$ || string_agg(quote_ident(data_type), ' int, ') || ' int)'
AS Stmt
FROM  (SELECT concat('subj_', id, '_', name) AS data_type FROM Subject) x


stmt


SELECT * FROM crosstab(
     $$SELECT DISTINCT ON (1, 2)
       j.reference, 'subj_'||j.subj||'_'||s.name AS data_type, SUM(j.value) AS val
       FROM Journal j
       JOIN Subject s ON s.id = j.subj
       GROUP BY j.reference, j.subj, s.name
       ORDER BY j.reference$$

    ,$$VALUES ('subj_1_fruit'), ('subj_2_drink'), ('subj_3_vege'), ('subj_4_fish')$$)
AS x (reference text, subj_1_fruit int, subj_2_drink int, subj_3_vege int, subj_4_fish int)



SELECT 1


SELECT * FROM crosstab(
     $$SELECT DISTINCT ON (1, 2)
       j.reference, 'subj_'||j.subj||'_'||s.name AS data_type, SUM(j.value) AS val
       FROM Journal j
       JOIN Subject s ON s.id = j.subj
       GROUP BY j.reference, j.subj, s.name
       ORDER BY j.reference$$

    ,$$VALUES ('subj_1_fruit'), ('subj_2_drink'), ('subj_3_vege'), ('subj_4_fish')$$)
AS x (reference text, subj_1_fruit int, subj_2_drink int, subj_3_vege int, subj_4_fish int)


reference
subj_1_fruit
subj_2_drink
subj_3_vege
subj_4_fish


bar
45
25
null
40

baz
20
25
null
null

foo
30
null
null
30



SELECT 3