join($join, $condition = null, $type = 'INNER');
$join : 關聯的表名;
$condition : 條件;
$type : JOIN類型;
用法舉例 :
~~~
db('Group')->alias('g')
->join('demo d','g.group_id=d.group_id')
->where("g.uid='$uid' and d.type='$type' and !isnull(extend_id)")
->column('extend_id');
~~~