sql 問題

group by 是用來找每一種類的平均數Avg(),總數Sum(),最大數Max(),最小數Min(), Count(), First(), Last(), etc.

select team,avg(age) as avg_age from emp group by team
找每一team的平均年齡

select team,count(*) as emp_no from emp group by team
找每一team的人數

select team,name,age from emp
要顯示每個 team 的name, age,不需要用group by

select team,name,age from emp group by team,name,age
如果兩人的team, name, age相同,group by只顯示一個結果