mysql not in用法

 select * from zan where uid not in(select uid from zan where zhongjiang !=0) group by uid order by rand() limit 40

不過這個執行效率比較低，正在找更好用的方法

 

 

我覺得還是不如兩條語句分開來寫，先查出所有的uid，然后再用not in  這樣查詢速度快很多

$sql="select uid from zan where zhongjiang !='0'";
$res=$dbs->query($sql);
$uid='';
while($o=$dbs->fetch_object($res)){
    $uid.=$o->uid.',';
}
$uid=substr($uid,0,strlen($uid)-1);
$sql="select * from zan where uid not in($uid) group by uid order by rand() limit 40";
$res=$dbs->query($sql);
$arr=array();
while($o=$dbs->fetch_object($res)){
    $arr[]=$o;
}