mysql - How to implement multi-table association query?

Question

Table A
LogID    UserId    Date
00001    0001      05-01
00002    0002      05-02
00003    0003      05-02
00004    0004      05-02
00005    0003      05-03
00006    0001      05-03  
00007    0002      05-03

Table B
UserId    Status
0001      Active
0002      Active  
0003      Active
0004      Inactive

Table C
UserId    Province
0001      Yunnan
0002      Fujian  
0003      Fujian
0004      Beijing

The above are three tables in the database, related through UserID. Table A is a user login information table with LogID as the primary key; Table B stores user active status, and Table C stores user geographical location information. Now I want to get the cumulative sum of the number of other states based on the date grouping in table A. The expected return result is:

Date    Active    Inactive    Yunnan    Fujian    Beijing
05-01   1         0           1         0         0   
05-02   2         1           0         2         1   
05-03   3         0           1         2         0

Can it be implemented with a SQL statement?

Answer 1

The business logic of this table is very loose, so I won’t write it for you in a loose way. Just treat your ABC table relationship as many-to-one:

select 
    a.date,
    sum(case when b.status='Active' then 1 else 0 end) 'Active',
    sum(case when b.status='Inactive' then 1 else 0 end) 'Inactive',
    sum(case when c.province ='Yunnan' then 1 else 0 end) 'Yunnan',
    sum(case when c.province ='Fujian' then 1 else 0 end) 'Fujian',
    sum(case when c.province ='Beijing' then 1 else 0 end) 'Beijing'
 from a left join b on a.userid=b.user_id join c on a.user_id=c.user_id 
 group by a.date order by a.date;