mysql - 如何检查mysql行中是否有值？

Question

抱歉我的英语不好

我想问一下如何检查行中是否有值？

提前致谢:)

Private Sub uploadpic()

    Dim SQLCmd As New MySqlCommand("SELECT Picture FROM Student_information WHERE S_I_D = ('" & ListView1.Items(ListView1.FocusedItem.Index).SubItems(0).Text & "') ", dbcon)

    dbcon.Open()

    *Dim pictureData As Byte() = DirectCast(SQLCmd.ExecuteScalar(), Byte())*

    dbcon.Close()

    Dim picture As Image = Nothing

    'Create a stream in memory containing the bytes that comprise the image.

    Using stream As New IO.MemoryStream(pictureData)
        'Read the stream and create an Image object from the data.
        PictureBox4.Image = Image.FromStream(stream)
    End Using


End Sub

Answer 1

SQLCmd.ExecuteScalar()如果结果集为空，将返回空引用。因此，您可以检查该值以了解行中是否有值。