Inner join on more than 2 tables - mysql

Question

I have 3 different tables balance,received,expenses with following data in it.
Table received:
mysql> select * from received;
+-----+---------+-----------------+---------------------+
| rid | site_id | received_amount | receive_date |
+-----+---------+-----------------+---------------------+
| 1 | 1 | 500 | 2015-08-19 18:16:51 |
| 2 | 1 | 600 | 2015-08-19 18:16:52 |
| 3 | 1 | 500 | 2015-08-20 18:16:52 |
| 4 | 1 | 500 | 2015-08-19 18:16:52 |
+-----+---------+-----------------+---------------------+
Table expenses:
mysql> select * from expenses;
+-----+---------+----------------+---------------------+
| eid | site_id | expense_amount | expense_date |
+-----+---------+----------------+---------------------+
| 1 | 1 | 500 | 2015-08-19 18:17:11 |
+-----+---------+----------------+---------------------+
Table balance:
mysql> select * from balance;
+----------------+---------+---------------+--------------+-----------------+-----------------+------+------+---------------------+
| transaction_id | site_id | account_title | particulars | opening_balance | closing_balance | rid | eid | transaction_date |
+----------------+---------+---------------+--------------+-----------------+-----------------+------+------+---------------------+
| 1 | 1 | test1 | test1 values | 0 | 500 | 1 | NULL | 2015-08-19 18:16:51 |
| 2 | 1 | test1 | test1 values | 500 | 1100 | 2 | NULL | 2015-08-19 18:16:52 |
| 3 | 1 | test1 | test1 values | 1100 | 1600 | 3 | NULL | 2015-08-20 18:16:52 |
| 4 | 1 | test1 | test1 values | 1100 | 1600 | 4 | NULL | 2015-08-19 18:16:52 |
| 5 | 1 | test1 | test1 values | 1600 | 1100 | NULL | 1 | 2015-08-19 18:17:11 |
+----------------+---------+---------------+--------------+-----------------+-----------------+------+------+---------------------+
I am trying to merge the amount of received and expenses into balance table using following query but somehow I am not able to get correct way to get it.
select
b.transaction_id,
b.site_id,
b.account_title,
b.particulars,
b.opening_balance,
r.received_amount,
e.expense_amount,
b.closing_balance,
b.transaction_date
from
balance b
inner join received r
on b.site_id = r.site_id
inner join expenses e
on b.site_id = e.site_id
group by
b.transaction_id;
I am trying to get this output
+----------------+---------+---------------+--------------+-----------------+-----------------+----------------+-----------------+---------------------+
| transaction_id | site_id | account_title | particulars | opening_balance | received_amount | expense_amount | closing_balance | transaction_date |
+----------------+---------+---------------+--------------+-----------------+-----------------+----------------+-----------------+---------------------+
| 1 | 1 | test1 | test1 values | 0 | 500 | NULL | 500 | 2015-08-19 18:16:51 |
| 2 | 1 | test1 | test1 values | 500 | 600 | NULL | 1100 | 2015-08-19 18:16:52 |
| 3 | 1 | test1 | test1 values | 1100 | 500 | NULL | 1600 | 2015-08-20 18:16:52 |
| 4 | 1 | test1 | test1 values | 1600 | NULL | 500 | 1100 | 2015-08-19 18:16:52 |
| 5 | 1 | test1 | test1 values | 1100 | 500 | NULL | 1600 | 2015-08-19 18:17:11 |
+----------------+---------+---------------+--------------+-----------------+-----------------+----------------+-----------------+---------------------+

Answer 1

You are somewhat close. Instead of INNER JOIN, You need to do a LEFT-JOIN to the receipts and expenses. Since your "Balance" table has ALL transactions, it will drive which entry it sees within your underlying support tables. Also, don't just join on the site ID, but just the "rID" and "eID" since they would be your primary keys on the table anyhow.
No need to group by transaction ID as that is the primary key in the balance table and would only have one entry by a given ID.
select
b.transaction_id,
b.site_id,
b.account_title,
b.particulars,
b.opening_balance,
r.received_amount,
e.expense_amount,
b.closing_balance,
b.transaction_date
from
balance b
LEFT join received r
on b.rid = r.rid
AND b.site_id = r.site_id
LEFT join expenses e
on b.eid = e.eid
AND b.site_id = e.site_id
order by
b.site_id,
b.transaction_date