求写一个sql，查询没有正确答案的试题id

[xuebo_xu]

试题选项表t_ems_item_option中有item_id试题id，option_id选项id，is_correct是否正确答案
例如

item_id option_id is_correct

试题1 a f
试题1 b f
试题1 c f
试题1 d t

试题2 a f
试题2 b f
试题2 c f
试题2 d f


求找到试题2

[熊心壮智]

SELECT item_id FROM t_ems_item_option where item_id not in (select item_id FROM t_ems_item_option where is_correct='t' ) group by item_id;

[楓VS痕]

select item_id from t_ems_item_option where is_correct='f' group by item_id having count(item_id)=4

[学海无涯-回头是岸]

两个sum 比较。相等，就是没有正确的。 select st from( select count(1) n1 ,st from T group by st) a join (select count(1) n2,st,iscorect from T group by st,iscorect) b on a.st＝b.st where a.n1=b.n2

[Rickshawboylu]

select item_id from t_ems_item_option where is_correct=false

[HipPop223]

SELECT
	 item_id
FROM t_ems_item_option
GROUP BY
	 item_id
HAVING
	 COUNT(item_id) = COUNT(IF(is_correct = 'f', item_id, NULL))

[yc_39]

SELECT 
  item_id
FROM
  t_ems_item_option
GROUP BY
  item_id
HAVING
  SUM(CASE WHEN is_correct = 't' THEN 1 ELSE 0 END) = 0