在2张桌子上选择UNION ALL，并选择Cases

Question

I'm running SQL Server 2005. I have 2 tables with the same columns but holding very different data.

SELECT *
FROM Table1 
WHERE ItemID IN ('4','2','1') 
ORDER BY 
    CASE  WHEN ItemID = 4 then 1 WHEN ItemID = 2 then 2 WHEN ItemID = 1 then 3 END 
UNION ALL 
SELECT * 
FROM Table2 
WHERE ItemID IN ('3','1','5','2') 
ORDER BY 
    CASE  WHEN ItemID = 3 then 4 WHEN ItemID = 1 then 5 WHEN ItemID = 5 then 6 WHEN ItemID = 2 then 7 END

I need to keep the order of the ItemID in the order that they are selected which is why I used CASE . This all works fine on each table but I can't find a way to combine them into 1 table of results with the results of each table ordered.

ie

4 (Table1)
2 (Table1)
1 (Table1)
3 (Table2)
1 (Table2)
5 (Table2)
2 (Table2)

Extremely grateful for any and all help.

Answer 1

Try this:

SELECT *
FROM (
    SELECT * , 1 as ord
    FROM Table1 
    WHERE ItemID IN (4, 2, 1) 
  UNION ALL 
    SELECT * , 2 as ord
    FROM Table2 
    WHERE ItemID IN (3, 1, 5, 2) ) t
ORDER BY  
    ord,
    CASE  WHEN ItemID = 3 then 4 WHEN ItemID = 1 then 5 WHEN ItemID = 5 then 6 WHEN ItemID = 2 then 7 END,
    CASE  WHEN ItemID = 4 then 1 WHEN ItemID = 2 then 2 WHEN ItemID = 1 then 3 END 

---

Or

SELECT *,
    ROW_NUMBER() OVER (ORDER BY ord,
        CASE  WHEN ItemID = 3 then 4 WHEN ItemID = 1 then 5 WHEN ItemID = 5 then 6 WHEN ItemID = 2 then 7 END,
        CASE  WHEN ItemID = 4 then 1 WHEN ItemID = 2 then 2 WHEN ItemID = 1 then 3 END) as RowNo 

FROM (
    SELECT * , 1 as ord
    FROM Table1 
    WHERE ItemID IN (4, 2, 1) 
  UNION ALL 
    SELECT * , 2 as ord
    FROM Table2 
    WHERE ItemID IN (3, 1, 5, 2) ) t

Answer 2

You can use the following query:

SELECT Table1.* , x.[Order] AS Ord
FROM Table1 
CROSS APPLY (SELECT CASE ItemID
                       WHEN 4 THEN 1 
                       WHEN 2 THEN 2 
                       WHEN 1 THEN 3 
             END) x([Order])  
WHERE ItemID IN ('4','2','1') 

UNION ALL 

SELECT Table2.* , y.[Order] AS Ord
FROM Table2 
CROSS APPLY (SELECT CASE ItemID 
                       WHEN 3 THEN 4 
                       WHEN 1 THEN 5 
                       WHEN 5 THEN 6 
                       WHEN 2 THEN 7 
                    END) y([Order])
WHERE ItemID IN ('3','1','5','2')
ORDER BY Ord

Calculated field [Order] guarantees that records from Table1 will come first, followed by records of Table2 . It also ensures ordering within each Table1 or Table2 partition.

Demo here

This is an alternative syntax without the use of CROSS APPLY :

SELECT Table1.*, 
       CASE ItemID
          WHEN 4 THEN 1 
          WHEN 2 THEN 2 
          WHEN 1 THEN 3 
       END AS Ord
FROM Table1 
WHERE ItemID IN ('4','2','1') 

UNION ALL 

SELECT Table2.*, 
       CASE ItemID 
          WHEN 3 THEN 4 
          WHEN 1 THEN 5 
          WHEN 5 THEN 6 
          WHEN 2 THEN 7 
       END AS Ord
FROM Table2 
WHERE ItemID IN ('3','1','5','2')
ORDER BY Ord

Demo here