mysql联表查询

SELECT a.*,b.UserAccount,c.companyName,d.AppName FROM appcreatecount a left JOIN " +
                    "userinfo b ON b.appuserid = a.appuserid LEFT JOIN proxyuserinfo c ON c.proxyId=b.UserProxyID " +
                    "LEFT JOIN userappsettingsystem d on d.appuserid = a.appuserid