Select values if doesn't match in other table by left join - mysql

Question

I am having some problem with getting the values from two tables of my database .
I have two tables in my database 1 is mem and 2nd is payment
mem stores name and drawid of users
payment table stores draw and instalment of the user
User pays us every month .
so if a user with a draw id 1 pays us in feb the values in two tables are
mem drawid=1 and name = something
payment draw = 1 and instalment=2
drawid in mem is same as draw in payment
so the tables has many to many relation.
Now I need to find the list of all the members who have not paid even 1 instalment before 4th month.
I am using this query
SELECT drawid,contact,dnd,mem.name, count(*) as numPayments FROM mem
LEFT JOIN payment ON (mem.drawid = payment.draw) GROUP BY
drawid HAVING numPayments < 4
it's working all good no issues only the issue is that I also need to show the instalments the user has paid so I need to fetch all the instalment from table payments and then show by while loop.
This query is perfect but it gives me repeated results !!!
SELECT drawid,contact,dnd,mem.name, count(*) as numPayments,NULL numPaidPayments ,NULL PAID_CONTACT,NULL NAME_PAID FROM mem
LEFT JOIN payment ON (mem.drawid = payment.draw) GROUP BY
drawid HAVING numPayments < 4
UNION
SELECT NULL drawid,NULL contact, NULL dnd, NULL name,NULL numPayments,COUNT(*) as numPaidPayments ,contact PAID_CONTACT,mem.name NAME_PAID FROM mem
INNER JOIN payment ON (mem.drawid = payment.draw) GROUP BY
drawid HAVING numPaidPayments >= 4

Answer 1

SELECT drawid,contact,dnd,mem.name, count(*) as numPayments,NULL numPaidPayments ,NULL PAID_CONTACT,NULL NAME_PAID FROM mem
LEFT JOIN payment ON (mem.drawid = payment.draw) GROUP BY
drawid HAVING numPayments < 4
UNION
SELECT NULL drawid,NULL contact, NULL dnd, NULL name,NULL numPayments,COUNT(*) as numPaidPayments ,contact PAID_CONTACT,mem.name NAME_PAID FROM mem
INNER JOIN payment ON (mem.drawid = payment.draw) GROUP BY
drawid HAVING numPaidPayments >= 4
Try above query.

Answer 2

Given this
MariaDB [sandbox]> select * from member;
+------+
| id |
+------+
| 1 |
| 2 |
| 3 |
| 4 |
+------+
4 rows in set (0.00 sec)
MariaDB [sandbox]> select * from payment;
+--------+------+
| mem_id | mth |
+--------+------+
| 1 | 1 |
| 1 | 2 |
| 1 | 3 |
| 1 | 4 |
| 2 | 1 |
| 2 | 3 |
| 3 | 2 |
| 3 | 4 |
+--------+------+
8 rows in set (0.00 sec)
This
select m.id, group_concat(p.mth order by p.mth) mthspaid,
sum(case when p.mem_id is not null then 1 else 0 end) NoofMthsPaid,
4 - sum(case when p.mem_id is not null then 1 else 0 end) NoofMthsMissed
from member m
left join payment p on p.mem_id = m.id
group by m.id
Gives this
+------+----------+--------------+----------------+
| id | mthspaid | NoofMthsPaid | NoofMthsMissed |
+------+----------+--------------+----------------+
| 1 | 1,2,3,4 | 4 | 0 |
| 2 | 1,3 | 2 | 2 |
| 3 | 2,4 | 2 | 2 |
| 4 | NULL | 0 | 4 |
+------+----------+--------------+----------------+
4 rows in set (0.00 sec)
And if you add in code to work out the months due
select paid.*, due.mthsmissed
from
(
select m.id, group_concat(p.mth order by p.mth) mthspaid,
sum(case when p.mem_id is not null then 1 else 0 end) NoofMthsPaid,
4 - sum(case when p.mem_id is not null then 1 else 0 end) NoofMthsMissed
from member m
left join payment p on p.mem_id = m.id
group by m.id
) paid
left join
(
select due.id, group_concat(due.mth order by due.mth) MthsMIssed
from
(
select m.id,d.mth
from member m,(select 1 mth union select 2 union select 3 union select 4) d
) due
left join payment p on p.mem_id = due.id and p.mth = due.mth
where p.mth is null
group by due.id
) due on paid.id = due.id
You get this
+------+----------+--------------+----------------+------------+
| id | mthspaid | NoofMthsPaid | NoofMthsMissed | mthsmissed |
+------+----------+--------------+----------------+------------+
| 1 | 1,2,3,4 | 4 | 0 | NULL |
| 2 | 1,3 | 2 | 2 | 2,4 |
| 3 | 2,4 | 2 | 2 | 1,3 |
| 4 | NULL | 0 | 4 | 1,2,3,4 |
+------+----------+--------------+----------------+------------+
4 rows in set (0.04 sec)