T SQL 游标只更新具有相同值的行

Question

我正在使用 MS SQL 服务器并且我有以下 table 'tmp_AVG_Weekly_Sales':

RowID   SKU   Shop  Week   Avg_Value   LAMBDA    PMF      Value
  1     ABC   200    2       1          2        0.13     NULL
  2     DEF   250    2       2          4        0.018    NULL
  3     XYZ   300    3       3          6        0.0024   NULL

我需要根据以下逻辑计算值字段 - 我正在使用游标和循环：

DECLARE @CUMULATIVE AS FLOAT = 0;
DECLARE @COUNT AS INT = 0;
DECLARE @LAMBDA AS FLOAT;
DECLARE @RowID AS INT;
DECLARE @PoissonCursor AS CURSOR;
DECLARE @THRESHOLD AS FLOAT = 0.99;
DECLARE @PMF AS FLOAT --= EXP(-@LAMBDA)


SET @PoissonCursor = CURSOR FOR

SELECT RowID
FROM 
[tmp_AVG_Weekly_Sales]

OPEN @PoissonCursor;

FETCH NEXT FROM @PoissonCursor INTO @RowID;

WHILE @@FETCH_STATUS = 0

BEGIN

    SELECT @LAMBDA = LAMBDA FROM [tmp_AVG_Weekly_Sales] WHERE RowID = @RowID

    SELECT @PMF = PMF FROM [tmp_AVG_Weekly_Sales] WHERE RowID = @RowID

    WHILE (@CUMULATIVE < @Threshold)

    BEGIN
        SET @CUMULATIVE += @PMF
        SET @COUNT += 1
        SET @PMF = @PMF * (@LAMBDA / @COUNT)

        END

        UPDATE [tmp_AVG_Weekly_Sales] SET [Value] = @COUNT - 1 WHERE RowID = @RowID

    FETCH NEXT FROM @PoissonCursor  INTO @RowID;

END

但是，上面只是用相同的值填充值字段：

RowID   SKU   Shop  Week   Avg_Value   LAMBDA    PMF      Value
  1     ABC   200    2       1          2        0.13     6
  2     DEF   250    2       2          4        0.018    6
  3     XYZ   300    3       3          6        0.0024   6

当我期待以下内容时：

RowID   SKU   Shop  Week   Avg_Value   LAMBDA    PMF      Value
  1     ABC   200    2       1          2        0.13     6
  2     DEF   250    2       2          4        0.018    9
  3     XYZ   300    3       3          6        0.0024   12

我哪里错了？

Answer 1

您永远不会重置 @CUMULATIVE 或增加 @Threshold，因此 SET 调用块仅在第一次执行时执行，随后的每个 UPDATE 仅使用那些原始的值。

T SQL 游标只更新具有相同值的行

T SQL Cursor is only updating row with same value

sql-server

loops

tsql

cursor