mysql 取差集和取交集

SELECT    projectCustomerPhoneFROM    (        SELECT DISTINCT            cu.projectCustomerPhone        FROM            t_projectcustomers cu        WHERE            projectId = '1408776faf1446b2a16493af0d43dcef'        UNION ALL            SELECT                vr.phone            FROM                t_visitrecords vr            WHERE                projectId = '1408776faf1446b2a16493af0d43dcef'    )TEMP GROUP BY projectCustomerPhone HAVING COUNT(projectCustomerPhone) = 1 //如果取并集 数字为 2

sql中将两个数据全部展现，然后利用GROUP BY进行合并，如果当phone只存在一个的时候说明是差集了。