Select 来自 3 个不同表的数据分组并限制为 3

Question

I have 3 tables named as Referrals, Providers, Suppliers.

Suppliers table

| id | name 
| 1  | Supplier A
| 2  | Supplier B
| 3  | Supplier C
| 4  | Supplier D

Providers table

| id | name 
| 1  | Provider A
| 2  | Provider B
| 3  | Provider C
| 4  | Provider D

Referrals table

| id | client_name | provider_id | supplier_id  | created_at
| 1  | Client A    | 1           | 1            | 2021-01-20
| 2  | Client B    | 1           | 1            | 2021-01-21
| 1  | Client C    | 2           | 1            | 2021-01-22
| 1  | Client A    | 2           | 2            | 2021-01-23
| 1  | Client A    | 3           | 2            | 2021-01-24
| 1  | Client A    | 1           | 3            | 2021-01-24
| 1  | Client A    | 4           | 3            | 2021-01-25
| 1  | Client A    | 4           | 4            | 2021-01-26
| 1  | Client A    | 1           | 1            | 2021-01-20

I want to count the number of referrals by each provider by supplier (top 3) in a month this format below:

Result format should be:

| id | referral_count | provider_id | supplier_id  | created_at
| 1  | 3         | 1           | 1            | January
| 2  | 2         | 1           | 1            | January
| 1  | 1         | 2           | 1            | January
| 1  | 2         | 2           | 2            | January
| 1  | 3         | 3           | 2            | January
| 1  | 1         | 1           | 2            | January
| 1  | 2         | 4           | 3            | January
| 1  | 3         | 4           | 3            | January
| 1  | 4         | 1           | 3            | January

Thanks

Answer 1

If I understand correctly, you simply want a count() as a window function:

select r.*,
       count(*) over (partition by provider_id, supplier_id, year(created_at), month(created_at)) as referral_count
from referrals r;

Answer 2

You can use count(*) window function to achieve that if your mysql version is 8 or higher:

select 
    id,
    (count(client_name) over (partition by provider_id, supplier_id, year(created_at), monthname(created_at))) referral_count, 
    provider_id, supplier_id, monthname(created_at) created_at
from Referrals;

If you are using older version of MySQL then you can use below option with subquery:

select id ,
(select count(*) from Referrals rf where rf.provider_id=r.Provider_id and rf.supplier_id=r.supplier_id
 group by provider_id , supplier_id  ,year(created_at),monthname(created_at)) referral_count,provider_id , supplier_id  ,monthname( created_at) created_at
from Referrals r;

                                                                    

Output:

id	provider_id	supplier_id	referral_count	created_at
1	1	1	3	January
2	1	1	3	January
1	2	1	1	January
1	2	2	1	January
1	3	2	1	January
1	1	3	1	January
1	4	3	1	January
1	4	4	1	January
1	1	1	3	January