sql语句求问？

Question

数据表Buy，属性分别是产品product，部门department，时间time，那么“ 2014年销售部购买但是其他部门没有购买的产品 ”sql语句怎么写，我思考了半天，实在是想不出来。

Answer 1

SELECT * FROM Buy WHERE id not in(SELECT id where department != 'sell' and ? > time > ?) where ? > time > ? and department = 'sell';

Answer 2

select distinct product from buy where department = '销售部' and left(convert(varchar(10),time,120),4) = '2014' and
not exists(select distinct product from where department != '销售部' and left(convert(varchar(10),time,120),4) = '2014')
这个是sql server的写法，不确定mysql是不是一样的语法，如果上面的函数用法不一样，百度一下就可以了

Answer 3

--你没有表明部门department是什么类型，我这里默认为int型，销售部department=5
SELECT DISTINCT product FROM [Buy] 

WHERE department=5 AND time=2018 AND Title NOT IN
                                                (
                                                   SELECT DISTINCT product FROM [Buy] WHERE department<>5 AND time=2018
                                                )
--如果数据类型对不上转化一下就行了