问如何使用U-SQL用上面的数据填充空白单元格

EN

@data = SELECT A, LAST_VALUE(Col == "" ? null : Col) OVER (ORDER BY Key ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) AS Col FROM @input;

@tb1 = SELECT * FROM 
        ( VALUES
        (1, "Noah1"),
        (2, (string)null),
          (3, "Noah3"),
          (5, (string) null),
          (6, (string)null),
          (7, "Noah6"),
          (8, "Noah7")
        ) AS T(Timestamp, a);


@tb1 =
    SELECT Timestamp,
           [a],
           [a] != null && [a] != LEAD([a], 1) OVER(ORDER BY Timestamp ASC) AS aSwitch
    FROM @tb1;

@tb1 =
    SELECT Timestamp,
           [a],
           SUM(aSwitch ? 1 : 0) OVER(ORDER BY Timestamp ASC ROWS UNBOUNDED PRECEDING) AS aGrp
    FROM @tb1;

@tb1 =
    SELECT Timestamp,
           FIRST_VALUE([a]) OVER(PARTITION BY aGrp ORDER BY Timestamp ASC) AS aFilled
    FROM @tb1;

OUTPUT @tb1 TO "/test.csv" USING Outputters.Csv(outputHeader: true);

"Timestamp","aFilled"
1,"Noah1"
2,"Noah1"
3,"Noah3"
5,"Noah3"
6,"Noah3"
7,"Noah6"
8,"Noah7"

@tb1 = SELECT * FROM 
        ( VALUES
        ("Noah1"),
        ((string)null),
          ("Noah3"),
          ((string) null),
          ((string)null),
          ("Noah6"),
          ("Noah7")
        ) AS T(a);

@tb1 = SELECT 1 AS Timestamp,
              [a] 
            FROM  @tb1;