Question

我想让我的读者的结果能够在另一个SQL命令的WHERE子句中使用。我试图将读者放入一个变量中使用，但它不起作用。我之前从未使用过读者，所以我不知道它们是如何工作的。任何人都可以让我知道如何让读者的结果进入哪里声明？感谢。

代码：

        Dim courseSelectCom = New SqlCommand("select stuff((select ','+course_name from course where school= '" & schoolSelect & "' for xml path ('')),  1, 1, '')", connection)

        Dim reader = courseSelectCom.ExecuteReader()
        If reader.Read() Then
            Dim courseVar As String
            courseVar = "%" & reader("course_name") & "%"

            Using totalStudentCom = New SqlCommand("SELECT COUNT(student_ID) FROM student " & "course_name like @course", connection)
                totalStudentCom.Parameters.AddWithValue("@course", courseVar)
                Dim result = totalStudentCom.ExecuteScalar()
                 MessageBox.Show("Students for course = " & result.ToString)
            End Using
        End If

Answer 1

这里有几个问题首先你应该使用参数化查询而不是字符串连接来构建sql命令
打开DataReader时，秒除非您在连接字符串中指定了子串MultipleActiveResultSets=True;，否则连接对象无法提供其他命令

Dim courseSelectCom = New SqlCommand("select course_name from course where school= @school", connection)
courseSelectCom.Parameters.AddWithValue("@school", schoolSelect)
Dim reader = courseSelectCom.ExecuteReader()
if reader.Read() then
    Dim courseVar As String
    courseVar = "%" & reader("course_name") & "%"

    Using totalStudentCom = new SqlCommand("SELECT COUNT(student_ID) FROM student " & _
                                "course_name like @course", connection)
        totalStudentCom.Parameters.AddWithValue("@course", courseVar)
        Dim result = totalStudentCom.ExecuteScalar()
        MessageBox.Show("Students for course = " & result.ToString)
    End Using
End If

请记住，这仅适用于MARS is enabled

在SQL查询中使用SqlDataReader的结果

1 个答案: