我想知道a。*，c.name，… a.access等的含义。换句话说，当我在点和点的功能之前添加字母时，我指的是什么。

这是我发现这种情况的代码示例：

$query = "SELECT a.*, c.name as categoryname,c.id as categoryid, ".
         "c.alias as categoryalias, c.params as categoryparams".
        " FROM #__k2_items as a".
        " LEFT JOIN #__k2_categories c ON c.id = a.catid";

        $query .= " WHERE a.published = 1"
        ." AND a.access <= {$aid}"
        ." AND a.trash = 0"
        ." AND c.published = 1"
        ." AND c.access <= {$aid}"
        ." AND c.trash = 0"
        ;