（SQL）连接表并订购最终结果

Question

table1table2和table3有不同的列，但都有一个OrderDate列。我想从所有3个表中获得一组结果集，并且我希望最终结果集按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) 

这工作，但我想这个结果设置为orderdate进行排序，所以我补充一下：

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返回错误“ORDER BY项目必须出现在选择列表中，如果语句包含一个UNION，INTERSECT或EXCEPT操作符。“

如果我更换

select * 

通过

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

我得到同样的错误。

咦？谢谢。

Answer 1

我解决了使用公共表表达式的问题，这里是我做过什么：

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...] 

它取代无法避免*如果table1，table2,table3具有相同的列名称（例如ID），否则SQL Server会引发错误，说明JoinedTable.ID含糊不清：它无法知道这是否意味着table1.ID或table2.ID或table3.ID。

Answer 2

尝试这个

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