sql-server - 在 VB.NET 中获取 SQL Server 表中的行数

Question

primary_student_table中有 10 行。

当我执行以下代码时，结果是-1。

Dim count As Int16
con.Open()
query = "SELECT COUNT(roll) AS rollcount FROM primary_student_table WHERE admityear = 2011 AND batch = 1 "

cmd = New SqlCommand(query, con)

count = cmd.ExecuteNonQuery
MsgBox(count)

con.Close()

上面的代码有什么问题吗？

Answer 1

您应该使用 ExecuteScalar() 而不是 ExecuteNonQuery()，因为您正在获取一个值。

count = Convert.ToInt16(cmd.ExecuteScalar())
MsgBox(count.ToString())

• SqlCommand.ExecuteScalar Method

正确编码

• 使用 using 语句进行正确的对象处置
• 使用try-catch block 正确处理异常

示例代码:

Dim connStr As String = "connection string here"
Dim query As String = "SELECT COUNT(roll) AS rollcount FROM primary_student_table WHERE admityear = 2011 AND batch = 1"
Using conn As New SqlConnection(connStr)
    Using cmd As New SqlCommand()
        With cmd
            .Connection = conn
            .CommandText = query
            .CommandType = CommandType.Text
        End With
        Try
            conn.Open()
            Dim count As Int16 = Convert.ToInt16(cmd.ExecuteScalar())
            MsgBox(count.ToString())
        Catch(ex As SqlException)
            ' put your exception here '
        End Try
    End Using
End Using