Question

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

我想知道，有没有办法克隆GREATEST的功能，保持在SQL标准内？

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

完全查询：

  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

您可以使用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

Answer 2

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

可以成为

(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

Answer 3

截至目前，Azure SQL 支持 GREATEST() 和 LEAST()。 SQL Server 2021（如果这就是它的名字）将用于本地安装。

最好的文档：

https://docs.microsoft.com/en-us/sql/t-sql/functions/logical-functions-greatest-transact-sql?view=sql-server-ver15

SQL标准中最好的和最少的

3 个答案: