将COUNT和GROUP BY与多个JOIN表一起使用

Question

i want to JOIN multiple table and need to COUNT from multiple tables using GROUP BY

the tables less like this

table A

a_id | name          
------------         
1    | john           
2    | david
3    | anna

table B

b_id | b_title
--------------
1    | b1     
2    | b2     
3    | b3     

table C

c_id | c_title | b_id
------------------------
1    | c1      | 2
2    | c2      | 3
3    | c3      | 1
4    | c4      | 1

table D

d_id | d_title | c_id | a_id | cost
-----------------------------------
1    | d1      | 3    | 1    | 200
2    | d2      | 1    | 1    | 130
3    | d3      | 2    | 2    | 240
4    | d4      | 2    | 3    | 170
5    | d5      | 4    | 1    | 95

what i want is something like this

name | COUNT(b_id) | COUNT(d_id) | SUM(cost)
--------------------------------------------
john |      2      |      3      |   425
david|      1      |      1      |   240 
anna |      1      |      1      |   170

this is my query

SELECT a.name, COUNT(d.d_id), SUM(cost)
FROM a INNER JOIN d ON a.a_id = d.a_id
GROUP BY a.a_id

I tried but I could not get the correct result of COUNT(b_id)

Answer 1

You want to count distinct b_id :

SELECT
  a.name, 
  COUNT(DISTINCT c.b_id),
  COUNT(d.d_id),
  SUM(d.cost)
FROM d 
JOIN a ON a.a_id = d.a_id
JOIN c ON c.c_id = d.c_id
GROUP BY a.a_id;

Answer 2

Just add extra JOIN to the table c like this:

SELECT a.name, COUNT(d.d_id), COUNT(b_id), SUM(cost)
FROM a 
INNER JOIN d ON a.a_id = d.a_id
INNER JOIN c ON c.b_id = d.c_id
GROUP BY a.a_id, a.name