超过两列

Question

选择重复计数我有一个看起来像这样的数据：

school  district  crs_sbj crs_num crs_sec 
CANYON HIGH IRON DISTRICT ENGL  2010  213 
CANYON HIGH IRON DISTRICT ENGL  2010  214 
CANYON HIGH IRON DISTRICT ENGL  1010  110 
CANYON HIGH IRON DISTRICT MATH  1010  400 
WAYNE HIGH WAYNE DISTRICT MATH  1010  321 
WAYNE HIGH WAYNE DISTRICT MATH  1010  322 
WAYNE HIGH WAYNE DISTRICT ENGL  1010  500 

我想算在每个单独的高中提供的独特的类。 例如，我想看看：

count school 
    3  CANYON HIGH 
    2  WAYNE HIGH 

我怎么会去这样做呢？我理解一列的概念，但是两个怎么样？

Answer 1

试试这个：

select school, count(distinct crs_num) _count 
from table 
group by school; 

Answer 2

Select School, count(distinct crs_num) 
from table 
group by School 

Answer 3

我不确定什么构成一个独特的类。

; with aardvark (select distinct school, district, crs_sbj, crs_num 
    from T) 
select district, school, count(*) 
from aardvark 
group by school, district 

由于可以跨地区使用同一学校名称，因此我在分组中包括该地区。