how to check database already existed record in database using asp.net mvc

$("#colnm").change(function () {
    $.ajax({
        url: '@Url.Action("INDEX", "HOME")',
        type: "POST",
        context: document.body,
        data: { colnm: $(this).val() },
        success: function (data) {
        if (data) {
        }
        else {
            alert("this colnm already exist in system");
            $("#colnm").val("");
            }
},
        error: function (err) {
         console.log(err);
        }
    });
});

public JsonResult CheckValidColName(string colnm)
{
    bool status = false;
    try
    {
string SQL = "Usp_CheckValidColName '" + colnm + "'";
DataTable DT = GetDataQuery(SQL);
status = Convert.ToBoolean(DT.Rows[0]["Status"].ToString());
    }
    catch (Exception)
    {
        throw;
    }
    return Json(status, JsonRequestBehavior.AllowGet);
}

string ConString = System.Configuration.ConfigurationManager.ConnectionStrings["DefaultConnection"].ConnectionString;

public DataTable GetDataQuery(string SQL)
{
    DataTable DT = new DataTable();
    var conn = new SqlConnection(ConString);
    using (var cmd = conn.CreateCommand())
    {
        cmd.CommandText = SQL;
        cmd.CommandTimeout = 6000;
        SqlDataAdapter da = new SqlDataAdapter(cmd);
        conn.Close();
da.Fill(DT);
        da.Dispose();
        conn.Close();
    }
    return DT;
}

CREATE PROC USP_CHECKVALIDCOLNAME
@COLNM VARCHAR(50)
AS
BEGIN 
DECLARE @CNT INT 
SELECT @CNT= COUNT(*) FROM TBL_NM WHERE COLNM=@COLNM
SELECT CAST(CASE WHEN @CNT >0 THEN 0 ELSE 1 END AS BIT) AS STATUS 
END

OR:

CREATE PROC USP_CHECKVALIDCOLNAME
@COLNM VARCHAR(50)
AS
BEGIN
    SET NOCOUNT ON;
    IF NOT EXISTS(SELECT COLNM FROM TBL_NM
        WHERE COLNM = @COLNM)
    BEGIN
        SELECT 1 AS STATUS
    END
    ELSE
    BEGIN
        SELECT 0 AS STATUS
    END
END