（SQL）連接表並訂購最終結果

Question

table1table2和table3有不同的列，但都有一個OrderDate列。我想從所有3個表中獲得一組結果集，並且我希望最終結果集按OrderDate排序。

(select * from table1 LEFT join table2 on 0=1 LEFT join table3 on 0=1 
    where somedate <= table1.orderdate) 

union all 

(select * from table1 RIGHT join table2 on 0=1 LEFT join table3 on 0=1 
    where somedate <= table2.orderdate) 

union all 

(select * from table1 RIGHT join table2 on 0=1 RIGHT join table3 on 0=1 
    where somedate <= table3.orderdate) 

這工作，但我想這個結果設置爲orderdate進行排序，所以我補充一下：

order by case when table1.orderdate is not null then table1.orderdate 
       when table2.orderdate is not null then table2.orderdate 
       else table3.orderdate end 

SQL Server返回錯誤「ORDER BY項目必須出現在選擇列表中，如果語句包含一個UNION，INTERSECT或EXCEPT操作符。「

如果我更換

select * 

通過

select *, table1.orderdate, table2.orderdate, table3.orderdate 

我得到同樣的錯誤。

咦？謝謝。

Answer 1

我解決了使用公共表表達式的問題，這裏是我做過什麼：

WITH JoinedTable as 
(
    (select table1.col1 as t1col1, table2.col2 as t1col2 [etc...] 
     from table1 LEFT join table2 on 0=1 LEFT join table3 on 0=1 
     where somedate <= table1.orderdate) 

    union all 

    (select table1.col1 as t1col1, table2.col2 as t1col2 [etc...] 
     from table1 RIGHT join table2 on 0=1 LEFT join table3 on 0=1 
     where somedate <= table2.orderdate) 

    union all 

    (select table1.col1 as t1col1, table2.col2 as t1col2 [etc...] 
     from table1 RIGHT join table2 on 0=1 RIGHT join table3 on 0=1 
     where somedate <= table3.orderdate) 
) 

select *, case when t1orderdate is not null then t1orderdate 
       when t2orderdate is not null then t2orderdate 
       else t3orderdate end 
       AS DateForOrderingResultSet 
from JoinedTable order by DateForOrderingResultSet 

的

table1.col1 as t1col1, table2.col2 as t1col2 [etc...] 

它取代無法避免*如果table1，table2,table3具有相同的列名稱（例如ID），否則SQL Server會引發錯誤，說明JoinedTable.ID含糊不清：它無法知道這是否意味着table1.ID或table2.ID或table3.ID。

Answer 2

嘗試這個

Select * from 
((select * from table1 LEFT join table2 on 0=1 LEFT join table3 
    where somedate <= table1.orderdate) 

union all 

(select * from table1 RIGHT join table2 on 0=1 LEFT join table3  
    where somedate <= table2.orderdate) 

union all 

(select * from table1 RIGHT join table2 on 0=1 RIGHT join table3 
    where somedate <= table3.orderdate)) A 

Order by A.orderdate