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;
错误是因为mm
是子查询因子 (AKA CTE) 实例的名称,但如您所见:
SELECT m.instructor
FROM m
WHERE m.c = mm.cc;
您尚未声明mm
为m
实例的 JOIN。采用:
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
我想你是想找教课最多的老师。
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