Question

oracle where条件后接unique判断，可以吗？

select tid ,tname from t where unique(
select tid from c where c.tid=t.tid
)
教师表：T(tid,tname)，S,课程表：C（cid,cname,tid）
这条语句本意是想查询出只开设了一门课程的教师工号和姓名，但是oracle中好像不支持这种写法啊?

Answer 1

oracle 确实不支持这种写法。
用GROUP BY + HAVING 来实现吧

Answer 2

select c.tid,t.tname, count(c.cid) as cnt
from c, t
where c.tid = t.tid
group by c.tid,t.tname
having count(c.cid) = 1

Answer 3

select tid,tname from t where tid in (select tid from c group by tid having count(*)=1)