sql - SQL 标准中的 GREATEST 和 LEAST

Question

我的理解是 GREATEST() 和 LEAST() 不是 SQL 标准的一部分，但很常见。

我在想，有没有办法在 SQL 标准中克隆 GREATEST 的功能？

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

完整查询:

  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

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

可以变成

(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