SQL 标准中的 GREATEST 和 LEAST
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时间：2020-09-01 07:40:47 来源:igfitidea点击:
GREATEST and LEAST in SQL standard
提问by WalterJ89
My understanding is that GREATEST() and LEAST() are not part of the SQL standard, but are very common.
我的理解是 GREATEST() 和 LEAST() 不是 SQL 标准的一部分，但很常见。
I'm wondering, is there a way to clone the functionality of GREATEST keeping within the SQL standard?
我想知道，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
The fully query:
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
采纳答案by Aillyn
You can use the CASEexpression:
您可以使用以下CASE表达式：
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
回答by Never Sleep Again
GREATEST(1,2,3,4,5,6,7) AS number
can become
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
