Is this a proper MySql query - mysql

Question

Im trying to get the first 100 rows consisting of First Name, Last Name, Department Name, Title, Salary from the employee database but not sure if Im doing it correctly. I tried the query below and it seems to work but doesn't feel right specially since there are no ON statements for the last 2 joins. Is it correct and is there a more efficient way I can perform this query.
This is the link to the database tables graph to give you a idea of the database.
https://dev.mysql.com/doc/employee/en/images/employees-schema.png
My query that seems to work:
SELECT e.first_name, e.last_name, dpn.dept_name, t.title, s.salary
FROM employees e, dept_emp dp
INNER JOIN departments dpn
ON dp.dept_no = dpn.dept_no
INNER JOIN salaries s
INNER JOIN titles t
LIMIT 100;
I tried the code below but kept getting error "#1054 - Unknown column 'e.emp_no' in 'on clause' " starting for the second to last ON statement.
SELECT e.first_name, e.last_name, dpn.dept_name, t.title, s.salary
FROM employees e, dept_emp dp
INNER JOIN departments dpn
ON dp.dept_no = dpn.dept_no
INNER JOIN salaries s
ON e.emp_no = salaries.emp_no
INNER JOIN titles t
ON e.emp_no = t.emp_no
LIMIT 100;
Thanks!

Answer 1

You have no join clause between e table and dp table eg:
SELECT e.first_name, e.last_name, dp.dept_name, t.title, s.salary
FROM employees e
INNER JOIN dept_emp dp on e.emp_no = dp.emp_no
INNER JOIN departments dpn ON dp.dept_no = dpn.dept_no
INNER JOIN salaries s ON e.emp_no = s.emp_no
INNER JOIN titles t ON e.emp_no = t.emp_no
LIMIT 100;

Answer 2

Try it like this:
SELECT e.first_name, e.last_name, departments.dept_name, titles.title, salaries.salary
FROM employees e
INNER JOIN dept_emp
ON e.emp_no = dept_emp.emp_no
INNER JOIN departments
ON dept_emp.dept_no = departments.dept_no
INNER JOIN titles
ON e.emp_no = titles.emp_no
INNER JOIN salaries
ON e.emp_no = salaries.emp_no
LIMIT 100;

Answer 3

The "On" clause in inner join is optional. If you do not have "On" clause it means a "cross join".
If what you want is inner join, then you should have an "On" clause and specify which columns should equate.

Answer 4

SELECT e.first_name,
e.last_name,
departments.dept_name,
titles.title,
salaries.salary
FROM employees e
LEFT JOIN dept_emp
ON e.emp_no = dept_emp.emp_no
LEFT JOIN departments
ON dept_emp.dept_no = departments.dept_no
LEFT JOIN titles
ON e.emp_no = titles.emp_no
LEFT JOIN salaries
ON e.emp_no = salaries.emp_no
LIMIT 100;
try this one too because
INNER JOIN: returns rows when there is a match in all tables.
LEFT JOIN: returns all rows from the left table, even if there are no matches in the right table.