How to fix "1054 - unknown column on clause" - mysql

Question

I wrote a sql code to get the data from my MySQL database. but when i run sql query it returns an error.
How an I fix this. Im new to this and I googled but i cant find a solution.
1054 - Unknown column 'departments.department_id' in 'on clause'
SELECT
staff_data.first_name,
staff_data.middle_name,
staff_data.last_name,
staff_data.gender,
staff_data.civil_status,
staff_data.birthday,
staff_data.address_line_1,
staff_data.address_line_2,
staff_data.address_line_3,
staff_data.contact_no_1,
staff_data.contact_no_2,
staff_data.nationality,
staff_data.religion,
staff_data.email,
staff_data.is_deleted,
staff_data.nic_number,
staff_data.is_admin,
departments.department_name,
job_positions.position_name
FROM
departments,
employee_position
INNER JOIN job_positions ON job_positions.department_id =
departments.department_id
AND departments.department_id = job_positions.department_id
AND employee_position.position_id = job_positions.position_id
INNER JOIN staff_data ON employee_position.user_id =
staff_data.nic_number
WHERE
employee_position.is_valid = 1

Answer 1

Please don't mix old school join syntax with modern syntax (the latter which you should be using only). Here is your corrected query using modern join syntax:
SELECT
s.first_name,
s.middle_name,
s.last_name,
s.gender,
s.civil_status,
s.birthday,
s.address_line_1,
s.address_line_2,
s.address_line_3,
s.contact_no_1,
s.contact_no_2,
s.nationality,
s.religion,
s.email,
s.is_deleted,
s.nic_number,
s.is_admin,
d.department_name,
j.position_name
FROM departments d
INNER JOIN job_positions j
ON j.department_id = d.department_id
INNER JOIN employee_position e
ON e.position_id = j.position_id
INNER JOIN staff_data s
ON e.user_id = s.nic_number
WHERE
e.is_valid = 1;
The error you are seeing is probably coming from the fact that your use of old school join syntax put the MySQL parser into a certain mode, which is then not behaving as you expect subsequently.
Note that I also introduced table aliases, which makes the query easier to read.

Answer 2

Issue is with first join
SELECT
staff_data.first_name,
staff_data.middle_name,
staff_data.last_name,
staff_data.gender,
staff_data.civil_status,
staff_data.birthday,
staff_data.address_line_1,
staff_data.address_line_2,
staff_data.address_line_3,
staff_data.contact_no_1,
staff_data.contact_no_2,
staff_data.nationality,
staff_data.religion,
staff_data.email,
staff_data.is_deleted,
staff_data.nic_number,
staff_data.is_admin,
departments.department_name,
job_positions.position_name
FROM
departments,
employee_position
INNER JOIN job_positions ON
job_positions.department_id = <change to req col>
-- departments.department_id join between employee_position and job_positions, but join is on department table
AND departments.department_id = job_positions.department_id
AND employee_position.position_id = job_positions.position_id
INNER JOIN staff_data ON employee_position.user_id =
staff_data.nic_number
WHERE
employee_position.is_valid = 1