Add friends, database design and implementation

Database design:

CREATE table user (id int auto_increment,name varchar (),key  (ID));
Relationship table: CREATE TABLE friendrelation (id int  key  auto_increment,id_left Int (5 ),id_right Int (5));

Database Information Display:

Note: When inserting a database, ensure data, left Id_left < Id_right, this way to prevent data redundancy,

If, if not, add a friend to insert two data into the database

Query your friend's PHP code:

Query thinking Analysis: Find Id_left = ID to check, take the results out, then find id_right = ID to look for, and then combine the results two times, that is, the ID of all friends ....

<?PHP//Conncet to Database$mysqli=NewMysqli (' 127.0.0.1 ', ' root ', ' root ', ' friends ') or die(' Can not connect to Mysqli '); Use your own message$sql= ' Select Id_right from friendrelation where id_left=5 ';    Each query executes two queries, this is the first step; $result=$mysqli->query ($sql); $res=Array(); foreach($result  as $v){        $res[]=$v; }    $sql 2= ' Select Id_left from friendrelation where id_right=5 ';//This is the second step of the query, and then two times the structure of the query to join together; $result 2=$mysqli->query ($sql 2); foreach($result 2  as $v){        $res[]=$v; }    foreach($res  as $v){        foreach($v  as $key=$value) {            $sql 3= "SELECT name from user where id=$value"; $result 3=$mysqli->query ($sql 3); foreach($result 3  as $key=$value) {                Echo"Name is:".$value[' name ']. " \ n "; }         }             }

Add friends, database design and implementation