I have a database with 4 tables that i want to join but I'm getting the wrong result and i don't understand why
This is the mysql query i run
SELECT co_id, u_name, c_name, e_status
FROM users
INNER JOIN company_owners ON u_id = co_userFk
INNER JOIN company ON co_companyFk = c_id
INNER JOIN employees ON u_id = userFk WHERE c_id = "1"
This is the result i get
+------------+-------------+-----------+------------------+
| co_id | u_name | c_name | e_status |
+------------+-------------+-----------+------------------+
| 1 | Simon | SimonCorp | Chef |
| 1 | Simon | SimonCorp | Chef |
+------------+-------------+-----------+------------------+
This is the result i want
+------------+-------------+-----------+------------------+
| co_id | u_name | c_name | e_status |
+------------+-------------+-----------+------------------+
| 1 | Simon | SimonCorp | Chef |
+------------+-------------+-----------+------------------+
This is my database structure
Users
+------------+-------------+----------+------------------+
| u_id | u_name | u_address| u_email |
+------------+-------------+----------+------------------+
| 1 | Simon | street 1 | Simon@gamil.com |
| 2 | Andrew | street 2 | Andrew@gmail.com |
| 3 | Tom | street 3 | Tom@gmail.com |
| 4 | Charlie | street 4 | charlie@gmail.com|
+------------+-------------+----------+------------------+
Company
+------------+-------------+----------+--------------------------+
| c_id | c_name | c_address| c_email |
+------------+---------------+----------+------------------------+
| 1 | SimonCorp | street 1 | simoncorp@gamil.com |
| 2 | SimonotherCorp| street 2 |simonothercorp@gmail.com|
+------------+---------------+----------+------------------------+
Employees
+------------+-------------+----------+----------------------+
| e_id | companyFk | userFk | e_status |
+------------+-------------+----------+----------------------+
| 1 | 1 | 1 | Chef |
| 2 | 2 | 2 | employee |
| 3 | 2 | 1 | employee |
| 4 | 1 | 3 | employee |
+------------+-------------+----------+----------------------+
Simon is chef of first company and the employee in the second
Company_Owners
+------------+--------------+-------------+
| co_id | co_companyFk | co_userFk |
+------------+--------------+-------------+
| 1 | 1 | 1 |
| 2 | 2 | 1 |
+------------+--------------+-------------+
Simon owns both companies
If you need distinct (not repetead rows) you must add the distinct clause
SELECT distinct co_id, u_name, c_name, e_status
FROM users
INNER JOIN company_owners ON u_id = co_userFk
INNER JOIN company ON co_companyFk = c_id
INNER JOIN employees ON u_id = userFk WHERE c_id = "1"
It's because your table Employees is considering only u_id = userFk
as join condition.
The table Employees has 2 lines linked to this employee (Simon):
Employees
+------------+-------------+----------+----------------------+
| e_id | companyFk | userFk | e_status |
+------------+-------------+----------+----------------------+
| 1 | 1 | 1 | Chef |
| 2 | 2 | 2 | employee |
| 3 | 2 | 1 | employee |
| 4 | 1 | 3 | employee |
+------------+-------------+----------+----------------------+
So, for each line, will be project a result with Simon as the Company Owner, considering that joint.
To handle this, you could restrict the join to consider companyFK
too.
It would be like this:
SELECT co_id, u_name, c_name, e_status
FROM users
INNER JOIN company_owners ON u_id = co_userFk
INNER JOIN company ON co_companyFk = c_id
INNER JOIN employees ON (u_id = userFk and c_id = companyFk) WHERE c_id = "1"
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