如何在数据库中找到最近的值

Question

如何在数据库中查找最近的值，例如数据库中的值为：

将要测试的数据为-100，系统如何发出测试结果-100是字符A。

Private Sub Button4_Click(sender As Object, e As EventArgs) Handles Button4.Click
    Try
        Dim persen As String
        Dim nilai_banding, hasil As String
        Dim cek = TextBox1.Text
        Dim reng_atas = cek + 15
        Dim reng_bawah = cek - 15
        Dim per = " %"
        Dim kuadrat = "^2"
        Dim pixeluji = TextBox2.Text
        Dim pixelsampel = TextBox1.Text
        'Dim C = TextBox3.Text

        'If C > 315 Then
        'MessageBox.Show("Jumlah Pixel Terlalu Besar Untuk Di Verifikasi", "Informasi", MessageBoxButtons.OK, MessageBoxIcon.Information)
        'Else

        'conn.Open()
        Dim mDA As New MySql.Data.MySqlClient.MySqlDataAdapter("SELECT citra_karakter From karakter_plat WHERE pixel_putih='" & TextBox1.Text & "' or pixel_putih >='" & reng_atas & "' and pixel_putih >='" & reng_bawah & "'", conn)
        '("SELECT Nama,Tanda_Tangan,Nilai_Hitam,Jumlah_Pixel,Keterangan From tanda_tangan WHERE nama LIKE  '%" & TextBox7.Text & "%'", conn)

        Dim dt As New DataTable
        mDA.Fill(dt)
        'DataGridView1.DataSource = DataGridViewAutoSizeColumnMode.AllCells
        'DataGridView1.DataSource = dt

        CMD = New MySql.Data.MySqlClient.MySqlCommand("SELECT nama_huruf,pixel_putih,pixel_hitam,jumlah_pixel,biner_karakter, citra_karakter FROM karakter_plat WHERE pixel_putih='" & TextBox1.Text & "' or pixel_putih<='" & reng_atas & "' and pixel_putih>='" & reng_bawah & "'", conn)
        RD = CMD.ExecuteReader()
        RD.Read()

        If RD.HasRows Then

            Label1.Text = RD.Item(0)
            TextBox2.Text = RD.Item(1)
            'Dim foto As Byte() = RD.Item(5)

        End If

上面的语法产生输出-100 = N

我想要-100 = A。

Answer 1

我的回答是基于使用查询找到特定字段的字段的最近值：

SELECT *
FROM (
    SELECT
        *,
        ROW_NUMBER() OVER (ORDER BY ABS(@specificValue - valueField)) AS seq
    FROM
        aTable) t
WHERE
    (seq <= 1); --if you want to have n nearest values change `1` to `n`

使用此类型的查询（例如）会为-99提供-102而不是@specificValue = -100。

作为替代查询（在MySQL中）：

SELECT *
FROM aTable
ORDER BY
    ABS(-100 - pixel_putih)
LIMIT 1;