Question

I have four tables that contain some fields

1. user(id, name, email, password, .....)
2. policy1(id, userid, ....)
3. policy2(id, userid, ....)
4. policy3(id, userid, ....)

Now this is clear that user’s primary key (id) is foreign key in other three tables.

I want to fetch total number of tables against each user that contain user id in that table.

for example:

user id 1 has entry in any two tables, 
user id 2 has entry in three tables, 
user id 3 has entry in any single table

Result should be like

id    total
1     2
2     3
3     1

I tried using Left Join but that I could not get the expected result.

Answer 1

You can use a subquery to get the count for each user and then add the values together to get the final result. I am using a LEFT JOIN to return all user rows even if there is not a matching value in the other tables. If you only want the users with values in the other tables, then you can use an INNER JOIN:

select u.id,
  Coalesce(CntP1, 0) + Coalesce(CntP2, 0) + Coalesce(CntP3, 0) TotalCount
from `user` u
left join
(
  select count(*) CntP1, userid
  from policy1
  group by userid
) p1
  on u.id = p1.userid
left join
(
  select count(*) CntP2, userid
  from policy2
  group by userid
) p2
  on u.id = p2.userid
left join
(
  select count(*) CntP3, userid
  from policy3
  group by userid
) p3
  on u.id = p3.userid