MySQL中的左外部联接

Question

Is it possible to join these two tables to get the following result.

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Table Stats

Date         Cus_ID    Pur        Amount 
2015-02-01   2585711    2           100
2015-02-02   2585711    5           250
2015-05-03   2585711    8           400
2015-02-01   2585475    2           100
2015-02-02   2585475    5           250
2015-05-03   2585475    8           400 
 

 
 
 

Table Customer     
Reg_Date     Cus_ID    Gender   Country
2014-04-11   2585711    Male    Sweden
2015-02-01   2585475    Female  Sweden
 

 
 
 

Expected Result

Date        Cus_ID   Pur       Amount   Gender  Country
2014-04-11  2585711  NULL       NULL    Male    Sweden
2015-02-01  2585711  2          100     Male    Sweden
2015-02-02  2585711  5          250     Male    Sweden
2015-05-03  2585711  8          400     Male    Sweden
2015-02-01  2585475  2          100     Female  Sweden
2015-02-02  2585475  5          250     Female  Sweden
2015-05-03  2585475  8          400     Female  Sweden
 

 
 
 

if I use a left outer join to join the two tables, I get the following result

Date        Cus_ID  Pur Amt Gender  Country
2015-02-01  2585711 2   100 Male    Sweden
2015-02-02  2585711 5   250 Male    Sweden
2015-05-03  2585711 8   400 Male    Sweden
2015-02-01  2585475 2   100 Female  Sweden
2015-02-02  2585475 5   250 Female  Sweden
2015-05-03  2585475 8   400 Female  Sweden

My query:

Select 
if(a.Date IS NULL,b.reg_date,a.date) as Date,
b.cus_id,
pur,
Amount,
gender,
country
     from 
        (Select * from stats) as a
                 Left outer join
                      (select * from customer) as b
on a.cus_id = b.cus_id

Any help will be highly appreciated. Thanks!

Answer 1

I don't know if this is still relevant.

If the idea to show every date a customer was active, even if they didn't make a purchase, I'd start with a table that gives me all dates and customer pairs first.

select [date],[cust_id] 
into #activity
from stats
union
select [reg_date],[cust_id]
from customer


select t1.*, t2.pur, t2.amt
from #activity t1
left outer join stats t2 on 
t1.[date] = t2.[date] and t1.[cust_id] = t2.[cust_id]