求至少有2名讲师（Lecturer）的所在系的系主任姓名（SQL代码）表如图

求至少有2名讲师（Lecturer）的所在系的系主任姓名（SQL代码）表如图

select t.Tdept,t.Tdno,t1.Tname -–所在系，主任编号，主任名字
from Teacher t
join Teacher t1
on t.Tdno=T1.Tno --t表的系主任编号=t1表教师编号
where t.Ttitles='讲师'
group by t.Tdept,t.Tdno,t1.Tname
having count(*)>=2;

SELECT Tname
FROM Teacher
WHERE Ttitles = "讲师"
GROUP BY Tdept
HAVING COUNT(*)>=2;