PLUS GRAND et MOINS dans la norme SQL

Question

Ma compréhension est que GREATEST() et LEAST() ne font pas partie de la norme SQL, mais sont très courants.

Je me demande, est-il un moyen de cloner la fonctionnalité de plus grand maintien dans le standard SQL?

SELECT id, GREATEST(1,2,3,4,5,6,7) AS number FROM table 

La pleine requête:

SELECT SUBSTR(section,1,2) AS campus, 
      AVG(GREATEST(maximum - enrolled, 0)) AS empty 
    FROM sectionrun 
    WHERE coursenumber = '105' AND subject = 'ENGL' 
GROUP BY campus 

Answer 1

Vous pouvez utiliser l'expression CASE:

SELECT SUBSTR(section,1,2) AS campus, 
      AVG(CASE WHEN maximum - enrolled > 0 
        THEN maximum - enrolled 
        ELSE 0 
       END) AS empty 
    FROM sectionrun 
    WHERE coursenumber = '105' AND subject = 'ENGL' 
GROUP BY campus 

Answer 2

GREATEST(1,2,3,4,5,6,7) AS number 

peut devenir

(select max(tmp) from (
     select 1 tmp from dual 
     union all 
     select 2 tmp from dual 
     union all 
     select 3 tmp from dual 
     union all 
     select 4 tmp from dual 
     union all 
     select 5 tmp from dual 
     union all 
     select 6 tmp from dual 
     union all 
     select 7 tmp from dual 
)) AS number