小编Sco*_*ott的帖子

以下查询仅返回已有订单的区域的区域名称.

   SELECT r.RegionName,
          COUNT (DISTINCT o.uid)
     FROM Orders AS o
LEFT JOIN Customers AS c ON o.CustomerID = c.uid
LEFT JOIN Regions AS r ON c.Region = r.uid
    WHERE (r.RegionName NOT LIKE 'NULL') 
      AND (r.RegionName <> '') 
      AND (r.RegionName NOT LIKE 'Region 1') 
      AND (o.DateOrdered LIKE '7%2011%')
 GROUP BY r.RegionName
 ORDER BY r.RegionName

如何修改它以便即使"COUNT"为"0"时所有区域名称都会出现？