mysql - 如何在不执行两次SQL调用的情况下计算SQL中列中特定值的出现次数

Question

我有一张表:Judges(JName char(25), LawSchool char(25)).

我试图在一次 SQL 调用中检索哈佛大学的法官人数和耶鲁大学的法官人数。我知道我可以做到这一点

SQL 调用 1)

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

SQL 调用 2)

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

但有没有一种方法可以在一个中检索到耶鲁的法官人数和哈佛的法官人数SQL 调用但将它们存储在两个变量中，例如 cnt 和 cnt2？

Answer 1

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