SQL Query返回其中一个

Question

select DISTINCT first_name, last_name, picture, last_active, id_participante1, id_participante2, id_user, [message], dataHora from chat_b_users inner join utilizadores
on chat_b_users.id_participante2 = utilizadores.id_user
left join chat_talks on chat_b_users.id_chat = chat_talks.id_chat
where id_participante1 = 1
union all
select DISTINCT first_name, last_name, picture, last_active, id_participante1, id_participante2, id_user, [message], dataHora from chat_b_users inner join utilizadores 
on chat_b_users.id_participante1 = utilizadores.id_user
left join chat_talks on chat_b_users.id_chat = chat_talks.id_chat
where id_participante2 = 1 order by last_active DESC

如何选择不同的值？

我需要返回所有这些数据，即使是null，但每个用户，我该如何做到这一点？

结果：

正如你在图片中看到的，我有两个来自同一个用户的聊天，我只想要其中一个。

Answer 1

尝试此操作：在代码中添加列列表以标识要显示的行。

 SELECT first_name, last_name, picture, last_active, id_participante1, id_participante2, id_user, [message], dataHora
(
select DISTINCT first_name, last_name, picture, last_active, id_participante1, id_participante2, id_user, [message], dataHora ,
ROW_NUMBER (PARTITION BY <add_yr_colist> ORDER BY Last_Avtive DESC) AS RNUM 
from chat_b_users inner join utilizadores
on chat_b_users.id_participante2 = utilizadores.id_user
left join chat_talks on chat_b_users.id_chat = chat_talks.id_chat
where id_participante1 = 1 OR id_participante2 = 1
)TVC WHERE RNUM = 1

Answer 2

您需要使用UNIION代替UNION ALL，如下所示：

select DISTINCT first_name, last_name, picture, last_active, id_participante1, id_participante2, id_user, [message], dataHora from chat_b_users inner join utilizadores
on chat_b_users.id_participante2 = utilizadores.id_user
left join chat_talks on chat_b_users.id_chat = chat_talks.id_chat
where id_participante1 = 1
union 
select DISTINCT first_name, last_name, picture, last_active, id_participante1, id_participante2, id_user, [message], dataHora from chat_b_users inner join utilizadores 
on chat_b_users.id_participante1 = utilizadores.id_user
left join chat_talks on chat_b_users.id_chat = chat_talks.id_chat
where id_participante2 = 1 order by last_active DESC

UNION删除重复记录（结果中的所有列都相同），UNION ALL不。

Difference betwwen UNION & UNION ALL