Question

SELECT SUBSTRING(m.content,1,20) as content, 
       m.viewed, m.sent_date, 
       u.username 
FROM message m 
INNER JOIN user u 
ON u.userid = m.message_from
WHERE m.message_to = :userid

我对此查询的问题是它从同一用户名中选择多行。我只想让它为每个用户名选择一行。

我相信我使用DISTINCT？

我无法让它工作，有人可以帮助我！

感谢。

Answer 1

SELECT SUBSTRING(m.content,1,20) as content, m.viewed, m.sent_date, u.username 
FROM message m INNER JOIN user u ON u.userid = m.message_from
WHERE m.message_to = :userid GROUP BY u.userid

Answer 2

是的！您可以在用户名中使用distinct

SELECT Distinct( u.username ), SUBSTRING(m.content,1,20) as content, 
       m.viewed, m.sent_date           
FROM message m 
INNER JOIN user u 
ON u.userid = m.message_from
WHERE m.message_to = :userid

使用distinct仅检索指定字段的一行

2 个答案: