SQL选择问题

Question

我在尝试弄清楚如何创建查询时遇到问题... 假设我们有两个这样的表：

TABLE A
id - box1_id - box1count - box2_id - box2_count
1  - 1       - 100       - 2       - 111
2  - 2       - 222       - NULL    - NULL
3  - 2       - 333       - 3       - 1000

TABLE B
id_box - box_Name
1      - HELLO
2      - TEST
3      - HELP

我想编写一个查询类似的查询：

id_box - box_Name - box_sumcount
1      - HELLO    - 100
2      - TEST     - 666
3      - HELP     - 1000

box_sumcount是box1_count或box2_count的总和，基于box1_id或box2_id等于id_box ...

Answer 1

SELECT TableB.id_Box,TableB.Boxname, Sum(BC.BoxCount)
FROM TableB
INNER JOIN 
  (SELECT box1_id as boxid, box1Count as boxCount
   UNION 
   SELECT box2_id as boxid, box2Count as boxCount
  ) BC
 ON (TableB.id_box=BC.Boxid)
 GROUP BY TableB.id_Box, TableB.Boxname