如何將不同列數的兩個表結合在一起？

Question

這是我的查詢。

select id,sender_id,receiver_id,date_added,subject,book_id,message from trading_message where (receiver_id=1132 or receiver_id=66) and (sender_id=1132 or sender_id=66) 
union 
select id,sender_id,receiver_id,date_added,message,'A' as subject,'B' as book_id from personal_message where (receiver_id=1132 or receiver_id=66) and (sender_id=1132 or sender_id=66) order by date_added asc 

而我得到這樣的錯誤。 'where子句'中的未知列'A'

請幫忙。

Answer 1

試請將mysql的變量，而不是字符 'A' 像

@ VAR1爲主體

，而不是

'A' 爲主題

Answer 2

select id,sender_id,receiver_id,date_added,subject,book_id,message from trading_message where (receiver_id=1132 or receiver_id=66) and (sender_id=1132 or sender_id=66) 
union 
select id,sender_id,receiver_id,date_added,'A', 'B', null from personal_message where (receiver_id=1132 or receiver_id=66) and (sender_id=1132 or sender_id=66) order by date_added asc 

試試看..我想我按照正確的順序匹配你的列，每列都有適量......

Answer 3

這應該適用於MYSQL。

聯合中的重要規則之一：字段數必須相等。

select id,sender_id,receiver_id,date_added,message, subject,book_id, from trading_message where (receiver_id=1132 or receiver_id=66) and (sender_id=1132 or sender_id=66) 
union 
select id,sender_id,receiver_id,date_added,message,'','' from personal_message where (receiver_id=1132 or receiver_id=66) and (sender_id=1132 or sender_id=66) order by date_added asc 

注意：您不需要在你的第二子查詢的別名，發動機需要的字段名從你的第一選擇結果

Answer 4

我跑這對MS SQL Server中。我認爲其中一個問題是'B'被返回爲book_id，我在猜測是聯合查詢的第一部分中的一個int。正如「TheOneWhoPrograms」中提到的那樣，列也必須按順序排列。

Create Table dbo.trading_message 
(
id int 
,sender_id int 
,receiver_id int 
,date_added datetime 
,subject varchar(100) 
,book_id int 
,message varchar(1000) 
) 

Create Table dbo.personal_message 
(
id int 
,sender_id int 
,receiver_id int 
,date_added datetime 
,message varchar(1000) 
) 

select 
id 
,sender_id 
,receiver_id 
,date_added 
,subject 
,book_id -- <- I *guessing* this is an int 
,message 
from trading_message 
where (receiver_id=1132 or receiver_id=66) 
and (sender_id=1132 or sender_id=66) 

union 

select 
id 
,sender_id 
,receiver_id 
,date_added 
,'A' as subject 
,0 as book_id -- <- Changed this from 'B' to zero 
,message 
from personal_message 
where (receiver_id=1132 or receiver_id=66) 
and (sender_id=1132 or sender_id=66) 

order by date_added asc 

上面有兩列（或更具體地）以相同的順序