oracle 10g sql带子句编译错误

Question

编译错误说"mm"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

该错误是因为mm是Subquery Factoring(AKA CTE)实例的名称,但正如您所看到的:

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

您尚未声明mm为m实例的JOIN .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