我有两个表：
问题
id title
1 First question
2 Second question
3 Third question
答案
id text question_id
1 Answer1 1
2 Answer2 1
3 Answer3 2
我正在搜索返回未回答问题的查询（上例中的问题id:3）？谢谢
Select id, title from question A Left Join answer B on A.id=B.question_id where B.question_id is null
由于Mysql不支持MINUS（或者至少我不知道），您必须使用join
SELECT q.id
FROM questions q LEFT JOIN answers a
ON q.id = a.question_id
WHERE a.question_id is null
select id,title from questions where id NOT IN(select distinct(question_id) from answers)
mysql中的NOT IN将帮助您
试试这个：
select * from questions left outer join answers on questions.id = question_id
where question_id is null
select q.id,q.title from questions q where q.id NOT IN(select distinct(question_id) from answers)
未使用是安全查询以查找已回答的问题。