具有子句

Question

我正在使用带有附加表scott的默认oracle PROJECT数据库，该数据库有5列：projno，projname，budget，start_date，end_date。

我想选择特定年份中项目数量最多的月份。 在我的练习指导中，据说必须通过相关子查询来完成。

我知道如何使用uncorrelated subquery：

SELECT EXTRACT(month FROM end_date) as "Month", COUNT(*) as "No of projects"
FROM proj
WHERE EXTRACT(year FROM end_date) = 2016
GROUP BY EXTRACT(month FROM end_date)
HAVING COUNT(*) = (SELECT MAX(COUNT(*))
               FROM proj
               WHERE EXTRACT(year FROM end_date) = 2016
               GROUP BY EXTRACT(month FROM end_date))

这是我对correlated subquery的尝试-它不起作用：

SELECT (EXTRACT(month FROM end_date)), COUNT(*) as "liczba"
FROM proj p
WHERE EXTRACT(year FROM end_date) = 2016
GROUP BY EXTRACT(month FROM end_date)
HAVING COUNT(*) =  MAX (SELECT(COUNT(EXTRACT(month FROM proj.end_date)))
                FROM proj
                WHERE EXTRACT(month FROM proj.end_date) = EXTRACT(month FROM p.end_date) 
AND EXTRACT(year FROM proj.end_date) = 2016)