我要將資料寫入資料庫 為何無法將資料寫入資料庫的資料表myfriend ? 哪裡有錯?

// 加入好友按鈕的發送頁面

echo
" <input type='button' value='" . _MD_ADD_FRIEND . "' onClick=\"window.open('" . $index_dir . "add_friend.php?uid=" . $uid . "&fid=" . $fid . "','addFriend','width=50,height=50')\" />\n";

==========================================================

//接收的頁面 寫入資料庫資料表 myfriend

<?php

//如果使用者有登入且有接收到兩個變數
if(($_GET['uid'] == $xoopsUser->getVar('uid')) && !empty($_GET['fid'])){
$select_sql =
"SELECT COUNT(*) FROM " .
$xoopsDB->prefix("myfriend") .
" WHERE uid='" . $uid . "' AND fid='" . $fid . "'";
?>

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