mysql - SQL 查询中 (n) 的含义？

Question

SELECT COURSENAME
FROM COURSE C1
WHERE (1) IN
(SELECT COUNT(DISTINCT(C2.COURSEFEES))
FROM COURSE C2
WHERE C2.COURSEFEES > C1.COURSEFEES);

这个“WHERE (1) IN”是什么意思？

Answer 1

这是一种笨拙的写法:

WHERE (SELECT COUNT(DISTINCT C2.COURSEFEES)
       FROM COURSE C2
       WHERE C2.COURSEFEES > C1.COURSEFEES
      ) = 1

这是说有一个类(class)费用比记录中的费用高 -- 或者说该类(class)费用是第二大的。

将其视为:

WHERE C1.COURSEFEES = (SELECT C2.COURSEFEES
                       FROM COURSE C2
                       GROUP BY C2.COURSEFEES
                       ORDER BY C2.COURSEFEES DESC
                       LIMIT 1 OFFSET 1
                      )