联接两个表而不会丢失相关值 [英] join two tables without losing relevant values
问题描述
我有两个表,分别代表客户产品及其竞争对手产品的数据库:
I have two tables representing a database for customer products and its competitors' products:
tmp_match
-from_product_id和to_product_id分别表示客户产品和竞争对手产品之间的匹配.
tmp_match
- from_product_id and to_product_id representing matches between customer product and competitor product respectively.
tmp_price_history
-显示每个日期每个产品的价格.
tmp_price_history
- shows the price of each product per date.
我正在尝试编写一个查询,该查询将列出表tmp_price_history
中的所有日期.对于每个日期,我都希望根据表tmp_match
中的产品匹配对查看客户产品价格与竞争对手产品价格之间的关系,无论是否存在客户产品或竞争对手产品的价格历史记录或两者都有:
I am trying to write a query which will list all dates from table tmp_price_history
. For each date I want to see customer product price vs competitor product price according to product matches pairs in table tmp_match
, regardless of whether there was a price history record for customer product or competitor product or both:
如果两个价格都可以在特定日期使用-请在其列中同时列出两个价格
if both prices are available for a specific date - list them both in their columns
如果只有客户产品的记录-仅显示客户价格(并将竞争者列留空).
if there is only a record for customer product - show only customer price (and leave the competitor column blank).
如果仅存在竞争对手产品的记录,请在其栏中显示竞争对手的价格.
if there is only record for competitor product - show competitor price in its column.
预期结果:
date from_product_id to_product_id cust_price comp_price
1 1 11 99 95
2 1 11 98 94
1 1 12 92
2 1 12 91
2 2 108
我尝试使用以下查询来实现这一目标:
I tried to achieve that using this query:
select cust_hist.date, from_product_id, to_product_id, cust_hist.price as cust_price,comp_hist.price as comp_price
from tmp_match as matches
left join tmp_price_history cust_hist
on cust_hist.product_id = matches.from_product_id
left join tmp_price_history comp_hist
on comp_hist.product_id = matches.to_product_id
;
但它没有达到我的目标,如在 sql代码段.
but it doesn't achieve my goal as can be seen in this sql snippet.
推荐答案
我认为您正在寻找这个东西:
I think that you are looking for this:
select distinct *
from (SELECT date,
if(group_concat(distinct cust_price), from_product_id, null)as from_product_id,
if(group_concat(distinct comp_price), to_product_id, null) as to_product_id,
group_concat(distinct cust_price) as cust_price,
group_concat(distinct comp_price) as comp_price
FROM (select cust_hist.date,matches.from_product_id,
matches.to_product_id,cust_hist.price cust_price,
comp_hist.price comp_price
from tmp_match matches
inner join tmp_price_history cust_hist on matches.from_product_id = cust_hist.product_id
inner join tmp_price_history comp_hist on matches.to_product_id = comp_hist.product_id
WHERE comp_hist.date = cust_hist.date
union
select comp_hist.date,matches.from_product_id,
matches.to_product_id,null as cust_price,
comp_hist.price comp_price
from tmp_price_history comp_hist
join tmp_match matches
on matches.to_product_id = comp_hist.product_id # and matches.from_product_id is null
union
select cust_hist.date,matches.from_product_id,
matches.to_product_id,
cust_hist.price cust_price,
null comp_price
from tmp_price_history cust_hist
join tmp_match matches
on matches.from_product_id = cust_hist.product_id # and matches.to_product_id is null
order by DATE, from_product_id, to_product_id, cust_price, comp_price) as u
group by date,from_product_id,to_product_id) g
您对sql片段的想法很棒!
Your idea about sql snippet was great!
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