Oracle 10g中的SQL与条款编译错误

Question

在编译错误说“毫米”和“cc”是无效的标识符！

with m as (
  select instructor, 
         count(*) as c 
    from class 
group by instructor),
     mm as ( 
  select max(m.c) as cc 
    from m)
select m.instructor 
  from m 
 where m.c = mm.cc;

Answer 1

的错误是因为mm是子查询分解（AKA CTE）实例的名称，但可以看到：

SELECT m.instructor 
 FROM m 
WHERE m.c = mm.cc;

您还没有宣布mm为连接到m实例。使用：

WITH m AS (
    SELECT instructor, 
           COUNT(*) as c 
      FROM CLASS
  GROUP BY instructor),
     mm AS ( 
    SELECT MAX(m.c) as cc 
      FROM m)
SELECT m.instructor 
  FROM m
  JOIN mm ON mm.cc = m.c

Answer 2

我想你正试图获得最班导师。

你能不能用

Select m.instructor FROM (select instructor, count(*) as c from class group by instructor order by 2 desc) m where rownum = 1