带条件检查的 MySQL 查询

Question

我有一个包含用户详细信息的表格。 现在我需要执行一个满足以下条件的 MySQL 查询：

有两张桌子

1) 用户表 - 包含用户 ID、姓名、名字

2) 类别表 - 其中包含类别 ID、类别类型、分配的用户 ID

现在我想执行满足以下条件的查询

用户只能看到一个类型为 simple、complex 的类别，这些类别仅分配给他的用户 ID，而该类别不应分配给任何其他用户 ID。

任何人都请帮助我。

Answer 1

drop table if exists category;
create table category (id int, categorytype varchar(10), assignedUserId int);

truncate table category;
insert into category values
(1,'simple',1),
(2,'complex',1),
(3,'simple',2),
(4,'complex',3),
(5,'odd',1);


MariaDB [sandbox]> select * from users where id < 6;
+----+----------+----------+--------+---------------------+
| id | userName | photo    | status | ts                  |
+----+----------+----------+--------+---------------------+
|  1 | John     | john.png |      1 | 2016-12-08 13:14:24 |
|  2 | Jane     | jane.png |      1 | 2016-12-08 13:14:24 |
|  3 | Ali      |          |      1 | 2016-12-08 13:14:24 |
+----+----------+----------+--------+---------------------+
3 rows in set (0.00 sec)

MariaDB [sandbox]>
MariaDB [sandbox]> select u.*, c.*
    -> from users u
    -> join category c on c.assigneduserid = u.id
    -> where u.id = 1
    -> and c.categorytype not in (select c.categorytype from category c where c.assigneduserid <> 1);
+----+----------+----------+--------+---------------------+------+--------------+----------------+
| id | userName | photo    | status | ts                  | id   | categorytype | assignedUserId |
+----+----------+----------+--------+---------------------+------+--------------+----------------+
|  1 | John     | john.png |      1 | 2016-12-08 13:14:24 |    5 | odd          |              1 |
+----+----------+----------+--------+---------------------+------+--------------+----------------+
1 row in set (0.00 sec)

Answer 2

尝试这个：

SELECT *
FROM category c
where userid = 123
and not exists (
  select 1
  from category c2
  where c.userid <> c2.userid
  and c.categorytype = c2.categorytype 
);

请注意，与其他答案不同，此查询不需要在两个地方提及 id，因此是一个更通用的查询。

Answer 3

SELECT * FROM categories 
WHERE category_type = 'simple' OR 
      category_type = 'complex' AND // (edited after comment of Philipp)
      assinged_userid = (Your User ID Here)