将针对数据表的查询结果添加到Visual Basic中另一个数据表中的列

Question

问题：我已经使用SQL服务器数据库上的查询填充了数据表。 查询是：

Select ID, startDate, codeID, Param, 
(select top 1 startDate from myTable 
where ID='" & ID & "' and Param = mt.param and codeID = 82 and startDate >= '" & startDate & "' and startDate >=mt.startDate 
ORDER BY startDate)endTime, 
from myTable mt where ID = '" & ID & "' 
AND (startDate between '" & startDate & "' AND '" & endDate & "' AND (codeID = 81))

我想要一个称为duration的新列，该列将是endTime和startDate之间的差（以毫秒为单位）。 我不能仅将另一个子查询添加到上述查询中，因为在子查询运行之前endTime列不存在。

因此，有没有一种方法可以运行第一个查询以填充数据表，然后运行如下查询：

Select DateDiff(ms,endTime,startDate)

自行将其结果添加到我的数据表的新列中？

Answer 1

您始终可以将其嵌套在另一个查询中：

select *, datediff(ms, startDate, endTime)
from ( 
    <your existing query here>
) t

当我在这里时，似乎您需要在参数化查询中学习一课：

Dim result As New DataTable
Dim Sql As String = _
      "SELECT *, datediff(ms, startDate, endTime) FROM (" & _
      "SELECT ID, startDate, codeID, Param, " & _
          "(select top 1 startDate from myTable " & _
           "where ID= @ID and Param = mt.param and codeID = 82 and startDate >= @startDate and startDate >=mt.startDate " & _
           "ORDER BY startDate) endTime " & _ 
      " FROM myTable mt " & _
      " WHERE ID = @ID AND startDate between @startDate AND @endDate AND codeID = 81" & _
      ") t"

Using cn As New SqlConnection("connection string"), _
      cmd As New SqlCommand(sql, cn)

    cmd.Parameters.Add("@ID", SqlDbType.VarChar, 10).Value = ID
    cmd.Parameters.Add("@startDate", SqlDbType.DateTime).Value = Convert.ToDateTime(startDate)
    cmd.Parameters.Add("@endDate", SqlDbType.DateTime).Value = Convert.ToDateTime(endDate)

    cn.Open()
    Using rdr = cmd.ExecuteReader()
        result.Load(rdr)
        rdr.Close()
    End Using
End Using