添加朋友, 数据库设计 与 实现

用户信息表: 

create table user(
id int auto_increment,
name varchar(20),
primary key (id)
);

关系表: 
create table FriendRelation(
id int  primary key  auto_increment,
id_left int(5),
id_right int(5)
);

<?php
// conncet to database
$mysqli=new mysqli(‘127.0.0.1‘,‘root‘,‘root‘,‘friends‘) or die (‘Can not connect to mysqli‘);  // use your own message

    $sql=‘select id_right from friendrelation where id_left=5‘;  //每次查询执行两次查询 , 这个是第一步;
    $result=$mysqli->query($sql);
    $res=array();

    foreach($result as $v){
        $res[]=$v;
    }

    $sql2=‘select id_left from friendrelation where id_right=5‘; // 这个是第二步查询  ,  然后将两次查询的结构拼接到一起;
    $result2=$mysqli->query($sql2);

    foreach($result2 as $v){
        $res[]=$v;
    }

    foreach($res as $v){
        foreach ($v as $key => $value) {
            $sql3="select name from user where id=$value";
            $result3=$mysqli->query($sql3);

            foreach ($result3 as $key => $value) {
                echo "name is : ".$value[‘name‘]."\n";
            }
         }         
    }