Question

我是编程新手，所以在以下情况下我需要一些查询帮助。

用户表

uid (PK)| name  | score
------------------
   1    | john  | 20
   2    | mary  | 40
   3    | david | 60
   4    | nancy | 80

question_tb表

qid|question
-------------
1  | a     
2  | b     
3  | c     
4  | d

question_user表

quid | user_id (FK) | question_id (FK)
--------------------------------
1    | 1            | 1
2    | 2            | 1
3    | 1            | 2
4    | 3            | 3

如上所示，显示了数据库的表结构。 question_user表包含特定用户已回答的问题。我想以DESC方式获得未回答特定用户的问题列表。

Answer 1

以下查询应该给您用户未回答的问题。

SELECT *
FROM question_tb as q
LEFT JOIN question_user as qu on q.qid = qu.question_id AND qu.user_id = USER_ID_HERE
WHERE  qu.user_id IS NULL;

Answer 2

如果您想获得DESC中特定用户未回答的问题，请使用以下查询

SELECT * FROM questions WHERE qid NOT IN (SELECT question_id FROM `question_user` WHERE uid = USER-ID) ORDER BY qid DESC;

Answer 3

尝试一下：

样本数据：

create table users (uid int, name varchar(10), score int);
insert into users values
(1, 'john', 20),
(2, 'mary' , 40),
(3, 'david', 60),
(4, 'nancy', 80);
create table question_tb (qid int, question char(1));
insert into question_tb values
(1, 'a'),     
(2, 'b'),    
(3, 'c'),     
(4, 'd');   
create table question_user (quid int, user_id int, question_id int);
insert into question_user values
(1, 1, 1),
(2, 2, 1),
(3, 1, 2),
(4, 3, 3);

T-SQL：

select uid, qid from users u
cross join question_tb q
where not exists(
    select 1 from question_user
    where u.uid = user_id and q.qid = question_id)
order by uid, qid

MySQL SELECT查询在何处查找不在相关表中的记录

3 个答案: