mysql取差集、交集、并集

需求：从两个不同的结果集（一个是子集，一个是父集），字段为电话号码phone_number,找出父集中缺少的电话号码，以明确用户身份。
结合网上资料，整理sql如下：

//mysql取差集

select num FROM
(

select u.code_sn as id,u.phone_number as num from t1 b
left join t2 u
on b.from_user=u.code_sn
where b.to_account='1000' and b.json_info like '%09月份%'

union all

select u.code_sn as id,u.phone_number as num from t3 o
left join t2 u
on o.buyer_code_sn=u.code_sn
where o.seller_account_code_sn='1000' and o.json_info like '%09月份%' 

)t3
group by num having count(num)=1

//mysql取交集

select num FROM
(

select u.code_sn as id,u.phone_number as num from t1 b
left join t2 u
on b.from_user=u.code_sn
where b.to_account='1000' and b.json_info like '%09月份%'

union all

select u.code_sn as id,u.phone_number as num from t1 o
left join t2 u
on o.buyer_code_sn=u.code_sn
where o.seller_account_code_sn='1000' and o.json_info like '%09月份%' 

)t3
group by num having count(num)=2

//mysql取并集

select num FROM
(

select u.code_sn as id,u.phone_number as num from t1 b
left join t2 u
on b.from_user=u.code_sn
where b.to_account='1000' and b.json_info like '%09月份%'

union all

select u.code_sn as id,u.phone_number as num from t1 o
left join t2 u
on o.buyer_code_sn=u.code_sn
where o.seller_account_code_sn='1000' and o.json_info like '%09月份%' 

)t3