计算字段以外部变量开头

Question

我有一个带有字段的表Tbl1：description，Dtype，valueLeft，valueRight 数据可能是这样的：

+----------------------------------------------+
| Description | Dtype | valueLeft | valueRight |
+----------------------------------------------+
| Art1        |   1   |     5     |       0    |
| Art2        |   1   |     3     |       0    |
| Art3        |   2   |     0     |       6    |
| Art4        |   1   |     11    |       0    |
| Art5        |   2   |     0     |       1    |
| ArtN        | ....  |    ....   |      ....  |
+..............................................+

字段Dtype只能是1或2

问题：我想用新值列进行SELECT值，其值为SUM值左移或值右值取决于字段Dtype的值（1 = sum valueLeft，2 =扣除valueRight）

示例：

+----------------------------------------------+
| Description | Dtype | valueLeft | valueRight | newcol
+----------------------------------------------+
| Art1        |   1   |     5     |       0    |    5
| Art2        |   1   |     3     |       0    |    8
| Art3        |   2   |     0     |       6    |    2
| Art4        |   1   |     11    |       0    |    13
| Art5        |   2   |     0     |       1    |    10

我该怎么做？

Answer 1

由于您没有使用SQL Server语法指定RDBMS ...

SELECT a.Description, a.Dtype, a.valueLeft, a.valueRight, 
            (SELECT SUM (CASE WHEN b.Dtype = 1 THEN b.valueLeft ELSE -b.valueRight END)
             FROM (
                    SELECT  ROW_NUMBER() OVER (ORDER BY Description) as id, Dtype, valueLeft, valueRight 
                    FROM Tbl1 ) b
             WHERE b.id <= a.id)
FROM (SELECT ROW_NUMBER() OVER (ORDER BY Description) as id,  Description, Dtype, valueLeft, valueRight 
      FROM Tbl1 ) a

demo here