子查詢SQL計數功能

Question

Jurisdiction  Route 
------------  ----- 
Portland   65 
Portland   55 
Cornelius   75 
Cornelius   75 
Cornelius   75 

如何計算cornelius的路由數量？答案是1

Answer 1

SELECT COUNT(*) 
FROM your_table 
GROUP BY Jurisdiction, Route 
WHERE Jurisdiction = 'Cornelius' 

或者

SELECT COUNT(DISTINCT Route) 
FROM your_table 
GROUP BY Jurisdiction 
WHERE Jurisdiction = 'Cornelius' 

Answer 2

你只需要使用COUNT()和DISTINCT

select count(distinct Jurisdiction) total, Jurisdiction 
from table1 
where Jurisdiction = 'Cornelius' 
group by Jurisdiction 

見SQL Fiddle with Demo