尝试从数据库中选择并插入默认值

Question

我试图弄清楚如何从数据库中选择并按下按钮时添加默认值。我要说的是，当按下按钮时会选择要插入默认值的表吗？

function budget_item($from_date, $to_date, $account) {
    $from = date2sql($from_date);
    $to = date2sql($to_date);

    $sql = "SELECT SUM(amount)
        FROM ".TB_PREF."budget
        WHERE account=".db_escape($account);
    if ($from_date != "")
        $sql .= " AND tran_date >= '$from' ";
    if ($to_date != "")
        $sql .= " AND tran_date <= '$to' ";
    $result = db_query($sql,"No budget were returned");

    $row = db_fetch_row($result);
    return $row[0];

    $sql = "INSERT INTO ".TB_PREF."budget(
            account) VALUES ('$date',
            ".db_escape($account).",".db_escape($amount).")";
}