如何計算SQL中列中某個特定值的出現次數，而無需執行兩次SQL調用

Question

我有一個表：判斷（JName char（25），LawSchool char（25））。

我試圖檢索出席哈佛大學的法官人數以及在一次SQL調用中出席耶魯大學的法官人數。我知道我能做到這一點

SQL CALL 1）

select LawSchool, count(*) as cnt from Judges where LawSchool = 'Harvard' 

SQL CALL 2）

select LawSchool, count(*) as cnt from Judges where LawSchool = 'Yale' 

但有沒有一種方法，我可以檢索誰參加耶魯法官人數以及參加的法官人數哈佛一 SQL調用但將它們存儲在兩個變量中，如cnt和cnt2？

Answer 1

select LawSchool, count(*) as cnt 
from Judges 
where LawSchool in ('Harvard','Yale') 
Group By LawSchool 

Answer 2

您可以通過

select LawSchool, count(*) as cnt 
from Judges where LawSchool in ('Harvard', 'Yale') 
group by LawSchool 

Answer 3

中和組使用您可以使用group by條款分離每獨特的價值合計結果：

SELECT LawSchool, COUNT(*) 
FROM  Judges 
WHERE LawSchool IN ('Harvard', 'Yale') 
GROUP BY LawSchool