PostgreSQL dotaz s dynamickými sloupci a počty od spojení

Jednoduchý dotaz na "Pokusy",

select student_id,sum(case when assessment_id=1 then 1 else 0 end) as "Assessment 1",
sum(case when assessment_id=2 then 1 else 0 end) as "Assessment 2",
sum(case when assessment_id=3 then 1 else 0 end) as "Assessment 3",
sum(case when assessment_id=4 then 1 else 0 end) as "Assessment 4",
sum(case when assessment_id=5 then 1 else 0 end) as "Assessment 5",
sum(case when assessment_id=6 then 1 else 0 end) as "Assessment 6"
from assessments_students
group by student_id
order by student_id

Ve funkci crosstab() je také potřeba explicitně definovat názvy sloupců jako "Posouzení 1", "Posouzení 2" a tak dále.

Nebo napište vlastní funkci pro vytvoření dynamického dotazu a spusťte ji pomocí příkazu EXECUTE.

DROP FUNCTION get_Attempts() ;

CREATE OR REPLACE FUNCTION get_Attempts() RETURNS text AS
$BODY$
DECLARE
        r1 record;
        str_query text := '';
 BEGIN
    str_query :='select student_id,';
    FOR r1 IN SELECT "_id" , "name" FROM Assessments
    LOOP
      str_query:= str_query || 
                  'sum(case when assessment_id=' || r1."_id" || ' then 1 else 0 end) as  "' || r1.name ||'",' ;
    END LOOP;
    str_query:=trim( trailing  ',' from str_query); -- remove last semicolon
    str_query:= str_query || ' from assessments_students group by student_id order by student_id';
    return str_query;
END
$BODY$
LANGUAGE 'plpgsql' ;

SELECT * FROM get_Attempts();

Druhý dotaz pro "prošlo"

select student_id,
max(case when assessment_id=1 and passed='t' then 't' else 'f' end) as  "Assessment 1",
max(case when assessment_id=2 and passed='t' then 't' else 'f' end) as  "Assessment 2",
max(case when assessment_id=3 and passed='t' then 't' else 'f' end) as  "Assessment 3",
max(case when assessment_id=4 and passed='t' then 't' else 'f' end) as  "Assessment 4",
max(case when assessment_id=5 and passed='t' then 't' else 'f' end) as  "Assessment 5",
max(case when assessment_id=6 and passed='t' then 't' else 'f' end) as  "Assessment 6" 
from assessments_students 
group by student_id 
order by student_id

a jeho funkce vypadá takto,

DROP FUNCTION get_passed() ;

CREATE OR REPLACE FUNCTION get_passed() RETURNS text AS
$BODY$
DECLARE
        r1 record;
        str_query text := '';
 BEGIN
    str_query :='select student_id,';
    FOR r1 IN SELECT "_id" , "name" FROM Assessments
    LOOP
      str_query:= str_query || 
                  'max(case when assessment_id=' || r1."_id" || ' and passed=''t'' then ''t'' else ''f'' end) as  "' || r1.name ||'",' ;
    END LOOP;
    str_query:=trim( trailing  ',' from str_query); -- remove last semicolon
    str_query:= str_query || ' from assessments_students group by student_id order by student_id';

    return str_query;
END
$BODY$
LANGUAGE 'plpgsql' ;

SELECT * FROM get_passed();