PHP向SQL添加注册 谁给小白解释下下面的if....esle 判断
$result = mysqli_query($conn,$sql);
//DQL: false 或 结果集
if($result===false){ //SQL执行失败
echo "<h3>SQL语句执行失败!</h3>";
echo "请检查SQL语法:$sql";
}else { //SQL执行成功
$row = mysqli_fetch_row($result); //抓取一行
if($row===null){ //未查询到任何记录
$now = time()*1000;
$sql = "INSERT INTO mail VALUES(NULL,'$phone','$pwd','$now')";
$result = mysqli_query($conn,$sql);
//DML: false 或 true
if($result===false){ //INSERT执行失败
echo "<h3>注册失败!</h3>";
echo "请检查SQL语法:$sql";
}else { //INSERT执行成功
echo "<h3>注册成功!</h3>";
echo "您在系统中编号为:".mysqli_insert_id($conn);
}
}else { //查询到一行记录
echo "<h3>注册失败!</h3>";
echo "原因:该手机号已经注册过!";
}
}