mysql 取差集和取交集

SELECT
    projectCustomerPhone
FROM
    (
        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。