mysql - 查询以检查表中的详细信息，如果找到则是，否则否

Question

以下是我的查询。这是正常工作的问题是，从类似的表中我无法检查特定用户是否不喜欢该元素。如果人喜欢显示是，如果不喜欢则显示否。

SELECT
      u_m.*,concat(usr.fname,' ',usr.lname) as NAME,
      u_m_u.sent_to,u_m_u.sent_by,u_m_u.shared_of,
      u_m_u.author,u_m_u.adddate

FROM user_message_users AS u_m_u
      LEFT JOIN user_messages AS u_m
        ON u_m.messageid = u_m_u.messageid
       LEFT JOIN smsusers AS usr
        ON u_m_u.sent_by=usr.id
       LEFT JOIN likes 
        ON u_m.messageid=likes.element_id 
        and
        likes.liked_by='1'
        group by u_m_u.messageid,u_m_u.sent_to
       ORDER BY u_m_u.adddate desc;

就像桌子一样

create table likes(
element_id varchar(100),
element_type varchar(100),
liked_by varchar(100), 
foreign key(liked_by) references smsusers(id)
 ON DELETE CASCADE ON UPDATE CASCADE,
adddate timestamp DEFAULT CURRENT_TIMESTAMP,
primary key(element_id,liked_by));

我的查询链接是

Answer 1

SELECT
      u_m.*,concat(usr.fname,' ',usr.lname) as NAME,
      u_m_u.sent_to,u_m_u.sent_by,u_m_u.shared_of,
      u_m_u.author,u_m_u.adddate,
      if (likes.element_id IS NULL, "No", "Yes") Likes

Answer 2

试试这个查询： -

SELECT
      u_m.*,concat(usr.fname,' ',usr.lname) as NAME,
      u_m_u.sent_to,u_m_u.sent_by,u_m_u.shared_of,
      u_m_u.author,u_m_u.adddate,if(likes.liked_by is null,'No','Yes')
as likees

FROM user_message_users AS u_m_u
      LEFT JOIN user_messages AS u_m
        ON u_m.messageid = u_m_u.messageid
       LEFT JOIN smsusers AS usr
        ON u_m_u.sent_by=usr.id
       LEFT JOIN likes 
        ON u_m.messageid=likes.element_id 
and
likes.liked_by='1'
group by u_m_u.messageid,u_m_u.sent_to
ORDER BY u_m_u.adddate desc;

试试SQLFiddle