SQL Query返回其中之一

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 

如何選擇不同的值？

我需要返回所有這些數據，即使是空值，但對每個用戶，我怎麼能做到這一點？

結果：

，你可以在圖片中看到，我已經從同一用戶進行的兩次聊天記錄，我只希望每個之一。

Answer 1

試試這個：在地方的代碼添加你的列清單（S），以確定要顯示哪一行。

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

您需要使用下面的UNIION代替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_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刪除重複記錄（其中在結果中的所有列都一樣），UNION ALL不。

Difference betwwen UNION & UNION ALL