三选二

Question

我创造了一个选择来让我的社区。

创建两个选择来获得我所关注的社区。

但我只有我的社区。

我没有得到我所关注的社区。

$user_id = $_GET["id"];

$row1 = array();
$row2 = array();

// get my communities

$res1 = mysql_query("SELECT * FROM communities where user_id = '$user_id'");

while($r1 = mysql_fetch_assoc($res1)) {
$row1[] = $r1;
   }

// get "id" of my communities I'm following 

$res = mysql_query("SELECT * FROM communities_follow where user_id = '$user_id'");

while($r = mysql_fetch_assoc($res)) {
    $coid = $r["coid"];

// get my communities I'm following 

$res2 = mysql_query("SELECT * FROM communities where id = '$coid'");

while($r2 = mysql_fetch_assoc($res2)) {
$row2[] = $r2;
   }


   }       

 $resp = array_replace_recursive($row1, $row2);

 print json_encode( $resp );

Answer 1

内在的加入只会让你得到那些社区，在那里你会跟随：

SELECT c.* FROM communities c 
INNER JOIN communities_follow cf ON c.id = cf.coid
WHERE cf.user_id = '$user_id';

或者，没有JOIN

SELECT * FROM communities
WHERE EXISTS (SELECT 1 FROM communities_follow cf
  WHERE c.id = cf.coid AND cf.user_id = '$user_id')

Answer 2

试试这个sql。

SELECT * FROM communities c LEFT JOIN communities_follow cf ON c.user_id = cf.user_id where
cf.user_id = '$user_id';