Question

我希望通过加入table_1中的userID来获取table_1中的所有表记录和table_2中的Username

“UserID保存在table_1中，列名为msg_from”

以下查询仅按用户提取一条记录。请帮我收到所有消息。

SELECT t1.id, t1.subject, t1.msg_from, t1.msg_date, t1.msg_status, t2.username
FROM table_1 AS t1, table_2 AS t2
WHERE t2.id = t1.msg_from

Answer 1

您应该能够通过类似于此的LEFT JOIN来实现这一目标：

"SELECT t1.id, t1.subject, t1.msg_from, t1.msg_date, t1.msg_status, t2.username 
 FROM table_1 AS t1 
 LEFT JOIN table_2 AS t2 ON t1.msg_from = t2.UserID"

从您发布的内容中确定t2上用户ID的字段名称是什么，所以我使用＆＃34; t2.UserID＆＃34;，但您可以轻松地将其替换为真实字段名称。如果您最终得到重复记录，则可以添加GROUP BY。

Answer 2

SELECT 
  t1.id, 
  t1.subject, 
  t1.msg_from, 
  t1.msg_date, 
  t1.msg_status, 
  t2.username 
FROM table_1 AS t1
LEFT JOIN  table_2 AS t2 
  ON t2.id = t1.msg_from

如果您的列名称为UserID，那么您可以将t2.UserID = t1.msg_from放在查询的最后一位。

Mysql连接查询帮助，不按要求工作

2 个答案: