我们要查询三个表以找出每个企业的客户数量和每个企业的记录数三个表是:businessDetails-------------------businessDetails.IDbusinessDetails.nameclientDetails-------------------clientDetails.IDclientDetails.businessDetailsIDrecords-------------------records.IDrecords.businessDetailsID我们能够同时从两个表中选择计数(businessDetails加上clientDetails或记录)