duplication de code dans les déclarations de cas sql

Question

Salut J'essaie de produire quelque chose comme ce qui suit, mais je constate qu'il y a beaucoup de duplication de code en cours.

| australian_has_itch | kiwi_has_itch | 
| yes     | no   | 
| no     | n/a   | 
| n/a     | no   | 

...

Ma requête ressemble à ceci avec deux déclarations de cas qui font la même chose, mais retournez le pays (ma vraie requête a 5 de ces déclarations de cas):

SELECT 
    CASE 
    WHEN 
     NOT EXISTS (
     SELECT person_id 
     FROM people_with_skin 
     WHERE people_with_skin.person_id = people.person_id 
     AND people.country = "Australia" 
    ) 
     THEN 'N/A' 
    WHEN 
     EXISTS (
     SELECT person_id 
     FROM itch_none_to_report 
     WHERE people.country = "Australia" 
     AND person_id = people.person_id 
    ) 
     THEN 'None to report' 
    WHEN 
     EXISTS (
     SELECT person_id 
     FROM itchy_people 
     WHERE people.country = "Australia" 
     AND person_id = people.person_id 
    ) 
     THEN 'Yes' 
    ELSE 'No' 
    END australian_has_itch, 

    CASE 
    WHEN 
     NOT EXISTS (
     SELECT person_id 
     FROM people_with_skin 
     WHERE people_with_skin.person_id = people.person_id 
     AND people.country = "NZ" 
    ) 
     THEN 'N/A' 
    WHEN 
     EXISTS (
     SELECT person_id 
     FROM itch_none_to_report 
     WHERE people.country = "NZ" 
     AND person_id = people.person_id 
    ) 
     THEN 'None to report' 
    WHEN 
     EXISTS (
     SELECT person_id 
     FROM itchy_people 
     WHERE people.country = "NZ" 
     AND person_id = people.person_id 
    ) 
     THEN 'Yes' 
    ELSE 'No' 
    END kiwi_has_itch, 
FROM people 

Y a-t-il un moyen pour moi de condenser cela d'une façon ou d'une autre et de ne pas avoir autant de duplication de code?

Merci!

Answer 1

Utilisation:

SELECT CASE 
      WHEN x.personid IS NOT NULL AND x.country = 'Australia' THEN 'N/A' 
      WHEN y.personid IS NOT NULL AND y.country = 'Australia' THEN 'None to report' 
      ELSE 'No' 
      END AS australian_has_itch, 
      CASE 
      WHEN x.personid IS NOT NULL AND x.country = 'NZ' THEN 'N/A' 
      WHEN y.personid IS NOT NULL AND y.country = 'NZ' THEN 'None to report' 
      ELSE 'No' 
      END AS australian_has_itch 
    FROM PEOPLE p 
LEFT JOIN (SELECT DISTINCT 
        pws.person_id, 
        p.country 
      FROM people_with_skin pws 
      JOIN PEOPLE p ON p.person_id = pws.person_id) x ON x.person_id = p.person_id 
LEFT JOIN (SELECT DISTINCT 
        intr.person_id, 
        p.country 
      FROM itch_none_to_report intr 
      JOIN PEOPLE p ON p.personid = intr.personid) y ON y.person_id = p.person_id