我有一个相当简单的查询，旨在显示已订阅的电子邮件地址数量以及未订阅的数量，按客户分组。查询:SELECTclient_id,COUNT(CASEWHENsubscribed=1THENsubscribedEND)ASsubs,COUNT(CASEWHENsubscribed=0THENsubscribedEND)ASunsubsFROMcontacts_emailAddressesLEFTJOINcontactsONcontacts.id=contacts_emailAddresses.contact_idGROUPBYclient_id相关表格的架构如下。contacts_email