SQL中如何加入3个表

Question

I have 3 tables:

Table 1

id | email
---+----------
1  |  a@a.com
2  |  b@a.com  
3  |  c@a.com 
4  |  d@a.com 

Table 2

order_id |   email    
---------+--------------
1        |   a@a.com       
2        |   a@a.com       
3        |   a@a.com       
4        |   c@a.com       
5        |   c@a.com       
6        |   b@a.com       
7        |   b@a.com       

Table 3

order_id |   sku    | qty
---------+----------+-----
1        |   sku1   | 1
2        |   sku1   | 2            
3        |   sku1   | 1            
4        |   sku2   | 3           
5        |   sku2   | 2            
6        |   sku2   | 6            
7        |   sku3   | 5           

I want to join table 1 to table 2 and table 3.

Get all rows of table 1 and table 3 sku1 + count qty by sku1 with email + count order of customer has 'sku1'

I want get a result like this:

id | email    | sku    | order    | orderqty
---+----------+--------+----------+--------------
1  |  a@a.com |  sku1  | 3        |   4
2  |  b@a.com |  sku1  | 3        |   5 
3  |  c@a.com |  sku1  | 1        |   6
4  |  d@a.com |  sku1  | null     |   null

Can someone help me? Thanks all <3

Answer 1

I think you want left join s and aggregation:

select t1.id, t1.email, 'sku1' sku, count(distinct t2.order_id) cnt_order, sum(t3.qty) orderqty
from table1 t1
left join table2 t2 on t2.email = t1.email
left join table3 t3 on t3.order_id = t2.order_id and t3.sku = 'sku1'
group by t1.id, t1.email