mysql join如何选择数据null

Question

我很少有这样结构的表

Promo_Validation

id | promo_id | validation_type | validation_value

Promo_Counter

id | promo_id | tanggal | counter | member_id | mid

Promo_Dtl

id | promo_id | min_amount_trx | max_amount_trx | cashback_type | cashback_value | max_cashback_value

Promo_Participants

id | promo_id | applied_to | created_date

顺便说一句，这些表格用于促销机制..
所以promo_counter 表将计算已经有促销交易的用户.. 如果他们还没有完成促销交易，则在该表上没有创建记录
promo_validation 和 promo_dtl 表格是保存促销条款和条件的地方
promo_participants table 是加入促销的商家保存的地方

所以，我正在尝试创建一个将它们全部加入的查询，我想显示促销机制数据以及每个用户的计数（用户使用当前促销的次数等）。我的查询看起来像这样

select pp.id as pp_id, pv.id as pv_id, pv.validation_type as pv_validationtype, pv.validation_value as pv_validationvalue,
pc.id as pc_id, pc.tanggal as pc_tanggal, pc.counter as pc_counter, pc.member_id as pc_memberid, pc.mid as pc_mid,
pd.min_amount_trx as pd_minamounttrx, pd.max_amount_trx as pd_maxamounttrx, pd.cashback_type as pd_cashbacktype, pd.cashback_value as pd_cashbackvalue, pd.max_cashback_value as pd_maxcashbackvalue
    from emoney_promo.promo_validation pv
    join emoney_promo.promo_counter pc on pv.promo_id = pc.promo_id
    join emoney_promo.promo_dtl pd on pd.promo_id = pv.promo_id
    join emoney_promo.promo_participants pp on pp.promo_id = pv.promo_id
    where pc.member_id = '0867667762'
    and pp.applied_to = '4518'
    and pc.mid = '4518';

当用户（在 member_id 列上）已经有 emoney_promo.promo_counter 表上的数据时，查询有效。但是当用户在 promo_counter 表中不可用时（该用户尚未完成促销交易），查询不会返回任何内容..

如果用户还没有完成任何促销（在上面的查询中，所以没有pc.member_id = 0867667762，我仍然可以获得结果吗？我的意思是，只需将null 给没有的列结果（来自 promo_counter 表），而不是什么都不返回？

对不起，如果我的话有点复杂顺便说一句:)

Answer 1

这个怎么样？

select pp.id as pp_id, pv.id as pv_id, pv.validation_type as pv_validationtype, pv.validation_value as pv_validationvalue,
pc.id as pc_id, pc.tanggal as pc_tanggal, pc.counter as pc_counter, pc.member_id as pc_memberid, pc.mid as pc_mid,
pd.min_amount_trx as pd_minamounttrx, pd.max_amount_trx as pd_maxamounttrx, pd.cashback_type as pd_cashbacktype, pd.cashback_value as pd_cashbackvalue, pd.max_cashback_value as pd_maxcashbackvalue
    from emoney_promo.promo_validation pv
    left join emoney_promo.promo_counter pc on pv.promo_id = pc.promo_id and pc.mid = '4518' and pc.member_id = '0867667762'
    join emoney_promo.promo_dtl pd on pd.promo_id = pv.promo_id
    join emoney_promo.promo_participants pp on pp.promo_id = pv.promo_id
    where pp.applied_to = '4518';