Question

SELECT login.id_user
     , username
     , SUBSTRING_INDEX
                ( GROUP_CONCAT
                       ( DISTINCT id_item 
                            ORDER 
                               BY items.ts_created
                       ),",",3
                ) grouped_items 
  FROM login
     , items 
 WHERE login.username LIKE '%%' 
   AND items.id_user = login.id_user 
   AND login.ts_deleted IS NULL 
   AND items.ts_deleted IS NULL 
 GROUP 
    BY login.id_user 
 ORDER 
    BY login.ts_created DESC

id喜欢从登录表中获取条目表中没有项目的条目。现在我写的查询抓住了3个最近的项目的用户。

我有这个抓取所有用户的查询。所以我想我试图将两个查询合并为一个。

SELECT id_user,username 
FROM login 
WHERE login.ts_deleted IS NULL 
ORDER BY ts_created DESC

Answer 1

如果您想要所有用户，则需要left join并且要非常小心on子句：

SELECT l.id_user, l.username,
       SUBSTRING_INDEX(GROUP_CONCAT(DISTINCT i.id_item ORDER BY i.items.ts_created), ',', 3) as grouped_items 
FROM login l LEFT JOIN
     items i
     ON i..id_user = l.id_user and i.ts_deleted IS NULL 
WHERE l.username LIKE '%%' 
      l.ts_deleted IS NULL 
GROUP BY l.id_user 
ORDER BY l.ts_created DESC

这个mysql查询有问题

1 个答案: