VB MySql AddWithValue 没有成功传递值 [英] VB MySql AddWithValue doesn't pass the value successfully

问题描述

我有以下VB代码

Dim cmd As New MySqlCommand("SELECT code FROM decoder WHERE ann_id = @aid", conn) 

cmd.Parameters.AddWithValue("@aid", 1)

Dim reader As MySqlDataReader = cmd.ExecuteReader()

reader.Read() 然后什么都不给我，但是，如果我用

The reader.Read() then gives me nothing, however, if I replace the code by

Dim cmd As New MySqlCommand("SELECT code FROM decoder WHERE ann_id = 1", conn) 

Dim reader As MySqlDataReader = cmd.ExecuteReader()

reader.Read() 给出了正确的结果.尝试使用 Add 代替，没有帮助.我在这里错过了什么?

reader.Read() gives the correct result. Tried using Add instead, doesn't help. What am I missing here?

非常感谢，

推荐答案

Private Sub ButtonInsert_Click(sender As Object, e As EventArgs) Handles ButtonInsert.Click
    Dim conn As New MySqlConnection
    Dim cmd As New MySqlCommand

    conn.ConnectionString = Me.Tag.ToString

    Try
        conn.Open()
        cmd.Connection = conn

        cmd.CommandText = "INSERT INTO myTable VALUES(NULL, @number, @text)"
        cmd.Prepare()

        cmd.Parameters.AddWithValue("@number", 1) 'sets @number to be numeric
        cmd.Parameters.AddWithValue("@text", "One") 'sets @text to be characters

        For i = 1 To 1000

            cmd.Parameters("@number").Value = i
            cmd.Parameters("@text").Value = "A string value"

            cmd.ExecuteNonQuery()
        Next
    Catch ex As MySqlException
        MessageBox.Show("Error " & ex.Number & " has occurred: " & ex.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
    End Try

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