mysql - 检索 User_ID 在 12 月而非 1 月进行交易的记录

Question

我有下表，我想选择在 12 月而非 1 月进行过交易的每个 user_id。

    User_Id  |Month     |Transaction_Id   |Transaction_Amount 
    ------------------------------------------------------------
    1       |Dec        |50               |452.36   
    1       |Jan        |51               |963.2   
    3       |Dec        |52               |499.3   
    4       |Jan        |53               |156.85   
    1       |Dec        |54               |145.63   
    3       |Dec        |55               |20.99   

执行查询后，该表应如下所示:

User_Id  |Month     |Transaction_Id   |Transaction_Amount 
------------------------------------------------------------
3       |Dec        |52               |499.3       
3       |Dec        |55               |20.99    

请注意，我需要使用一个高效的查询来过滤上述要求，因为这将应用于数千条记录。

Answer 1

有几种方法:

使用不存在:

select * from yourtable t
where month = 'Dec'
and NOT EXISTS (
    select null from yourtable t2
    where t2.user_id = t.user_id
    and t2.month = 'Jan')

使用 NOT IN()

select * from yourtable t
where month = 'Dec'
and user_id NOT IN (
    select t2.user_id from yourtable t2
    where t2.month = 'Jan')

使用左连接:

select t.* from yourtable t
left join yourtable t2 on t2.user_id = t.user_id and t2.month = 'Jan'
where t.month = 'Dec'
and t2.user_id IS NULL