3 table merge with some condition

I am new to this forum and I am learning mysql with the help of online resources, currently I am trying to compare and merge table with some conditions

Fiddle

These are my tables;

mysql> show tables;
         +--------------------+
         | Tables_in_products |
         +--------------------+
         | main_info          |
         | product1           |
         | product2           |
         +--------------------+
         3 rows in set (0.00 sec)

This is my first table

mysql> select * from main_info; 
         +------+------+-------+-------+----------+
         | key1 | key2 | info1 | info2 | date     |
         +------+------+-------+-------+----------+
         | 1    | 1    | 15    | 90    | 20120501 |
         | 1    | 2    | 14    | 92    | 20120601 |
         | 1    | 3    | 15    | 82    | 20120801 |
         | 2    | 1    | 17    | 90    | 20130302 |
         | 2    | 2    | 16    | 88    | 20130601 |
         +------+------+-------+-------+----------+
         5 rows in set (0.00 sec)

This is product table1 :

mysql> select * from product1;
         +------+------+--------+--------------+
         | key1 | key2 | serial | product_data |
         +------+------+--------+--------------+
         | 1    | 1    | 0      | 15.556       |
         | 1    | 1    | 1      | 14.996       |
         | 1    | 1    | 2      | 12.556       |
         | 1    | 1    | 3      | 15.669       |
         | 1    | 2    | 0      | 12.556       |
         | 1    | 2    | 1      | 13.335       |
         | 1    | 3    | 1      | 12.225       |
         | 1    | 3    | 2      | 13.556       |
         | 1    | 3    | 3      | 14.556       |
         | 2    | 1    | 0      | 12.556       |
         | 2    | 1    | 1      | 13.553       |
         | 2    | 1    | 2      | 12.335       |
         +------+------+--------+--------------+
         12 rows in set (0.00 sec)

This is second product table

```
mysql> select * from product2;
+-

As first step I merge the two product tables. I need an full outer join on product1 and product2 tables. To obtain on outer join in mysql we can union a left join and a right join. Start with a left join. In the following query IFNULL(p1.key1, p2.key1) is useful to merge two key column coming from the two product tables and IFNULL(, 'NaN') is useful to obtain 'NaN' in the output.

select IFNULL(p1.key1, p2.key1) as key1, 
       IFNULL(p1.key2, p2.key2) as key2,
       IFNULL(p1.serial, p2.serial) as serial,
       IFNULL(p1.product_data, 'NaN') as product_data1, 
       IFNULL(p2.product_data, 'NaN') as product_data2
from       product1 p1
left join  product2 p2 on p1.key1 = p2.key1 and p1.key2 = p2.key2 and p1.serial =     p2.serial;

To obtain a full outer join I need to repeat the previous query with 'right join' and union the result with the 'left join'

select IFNULL(p1.key1, p2.key1) as key1, 
       IFNULL(p1.key2, p2.key2) as key2,
       IFNULL(p1.serial, p2.serial) as serial,
       IFNULL(p1.product_data, 'NaN') as product_data1, 
       IFNULL(p2.product_data, 'NaN') as product_data2
from       product1 p1
left join  product2 p2 on p1.key1 = p2.key1 and p1.key2 = p2.key2 and p1.serial = p2.serial
union
select IFNULL(p1.key1, p2.key1) as key1, 
       IFNULL(p1.key2, p2.key2) as key2,
       IFNULL(p1.serial, p2.serial) as serial,
       IFNULL(p1.product_data, 'NaN') as product_data1, 
       IFNULL(p2.product_data, 'NaN') as product_data2
from       product1 p1
right join  product2 p2 on p1.key1 = p2.key1 and p1.key2 = p2.key2 and p1.serial = p2.serial;

For convenience, I create a view with the previous query:

create or replace view p12 as
select IFNULL(p1.key1, p2.key1) as key1, 
       IFNULL(p1.key2, p2.key2) as key2,
       IFNULL(p1.serial, p2.serial) as serial,
       IFNULL(p1.product_data, 'NaN') as product_data1, 
       IFNULL(p2.product_data, 'NaN') as product_data2
from       product1 p1
left join  product2 p2 on p1.key1 = p2.key1 and p1.key2 = p2.key2 and p1.serial = p2.serial
union
select IFNULL(p1.key1, p2.key1) as key1, 
       IFNULL(p1.key2, p2.key2) as key2,
       IFNULL(p1.serial, p2.serial) as serial,
       IFNULL(p1.product_data, 'NaN') as product_data1, 
       IFNULL(p2.product_data, 'NaN') as product_data2
from       product1 p1
right join  product2 p2 on p1.key1 = p2.key1 and p1.key2 = p2.key2 and p1.serial = p2.serial;

To check we can try with:

mysql> select * from p12 where key1 = 1 and key2 =1 ;
+------+------+--------+---------------+---------------+
| key1 | key2 | serial | product_data1 | product_data2 |
+------+------+--------+---------------+---------------+
| 1    | 1    | 0      | 15.556        | 5.556         |
| 1    | 1    | 1      | 14.996        | 4.996         |
| 1    | 1    | 2      | 12.556        | NaN           |
| 1    | 1    | 3      | 15.669        | NaN           |
+------+------+--------+---------------+---------------+

So the he final query is:

select mi.key1, mi.key2, p12.serial, mi.info1, mi.info2, mi.date, p12.product_data1, p12.product_data2 
from main_info mi 
inner join p12 on mi.key1 = p12.key1 and mi.key2 = p12.key2
order by mi.key1, mi.key2, p12.serial;

+------+------+--------+-------+-------+----------+---------------+---------------+
| key1 | key2 | serial | info1 | info2 | date     | product_data1 | product_data2 |
+------+------+--------+-------+-------+----------+---------------+---------------+
| 1    | 1    | 0      | 15    | 90    | 20120501 | 15.556        | 5.556         |
| 1    | 1    | 1      | 15    | 90    | 20120501 | 14.996        | 4.996         |
| 1    | 1    | 2      | 15    | 90    | 20120501 | 12.556        | NaN           |
| 1    | 1    | 3      | 15    | 90    | 20120501 | 15.669        | NaN           |
| 1    | 2    | 0      | 14    | 92    | 20120601 | 12.556        | 2.556         |
| 1    | 2    | 1      | 14    | 92    | 20120601 | 13.335        | 3.335         |
| 1    | 2    | 2      | 14    | 92    | 20120601 | NaN           | 2.56          |
| 1    | 2    | 3      | 14    | 92    | 20120601 | NaN           | 3.556         |
| 1    | 3    | 1      | 15    | 82    | 20120801 | 12.225        | 2.225         |
| 1    | 3    | 2      | 15    | 82    | 20120801 | 13.556        | 3.556         |
| 1    | 3    | 3      | 15    | 82    | 20120801 | 14.556        | NaN           |
| 2    | 1    | 0      | 17    | 90    | 20130302 | 12.556        | NaN           |
| 2    | 1    | 1      | 17    | 90    | 20130302 | 13.553        | NaN           |
| 2    | 1    | 2      | 17    | 90    | 20130302 | 12.335        | NaN           |
| 2    | 2    | 0      | 16    | 88    | 20130601 | NaN           | 2.556         |
| 2    | 2    | 1      | 16    | 88    | 20130601 | NaN           | 3.553         |
+------+------+--------+-------+-------+----------+---------------+---------------+

StackExchange Database Administrators Q#68013, answer score: 2