mysql查找最新用戶評論（第2部分）

Question

續。在mysql find recent user comments

而且，2個表：

create table user(
    userID int auto_increment, 
    userName varchar(10), 
    userCreatedDate timestamp, 
    primary key(userID) 
); 

create table comment(
commentID int auto-increment, 
userID int, 
comment varchar(100), 
primary key(commentID), 
foreign key(userID) references user(userID) 
); 

此番userCreateDate和commentID值是從第1部分
不同，我想找到從數據庫的最新評論。

我的輸出如下：

這裏是我試過的查詢：

select u.userID, max(c.commentID) as commentID, c.comment, u.userCreatedDate 
from comment c 
left join user u on c.userID = u.userID 
group by u.userID 
order by u.userCreateDate desc 

但是，我不能讓我的輸出。
有人可以幫助我嗎？

Answer 1

你可以做到這一點如下，被稱爲group wise max/minhttp://dev.mysql.com/doc/refman/5.7/en/example-maximum-column-group-row.html

select u.*,c.comment from user u 
join comment c on c.userID = u.userID 
join (
select max(commentID) as commentID,userID 
from comment group by userID 
)c1 on c1.commentID = c.commentID 

Answer 2

嘗試此查詢： -

select u.userID,commentID, c.comment, u.userCreatedDate 
from comment c 
left join user u on c.userID = u.userID 
WHERE commentID=(SELECT MAX(c2.commentID) 
       FROM comment c2 
       WHERE c.userID = c2.userID)