mysql-连接两个表而不会丢失相关值

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：

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_price_history-显示每个日期每个产品的价格.

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,而不管是否存在客户产品或竞争对手产品的价格历史记录,或者是否两者都有：

如果两个价格在特定日期都可用-将它们都列在它们的列中

如果只有客户产品的记录-仅显示客户价格(并将竞争对手列留空).

如果只有竞争对手产品的记录,请在其栏中显示竞争对手的价格.

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点：

 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
;

但这没有达到我的目标,正如在sql snippet中可以看到的那样.

解决方法:

我认为您正在寻找：

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

关于sql片段的想法很棒！

标签：data-analysis,sql,mysql,join
来源： https://codeday.me/bug/20191010/1884828.html