Select value in table if it exists in another - mysql

Question

I am trying to get all the values from a users table where a specific company name is found.
I also need to get the rows in the users table where that same company name is in another table and matches the name in users table
I have 2 tables like this:
Table: Users.
USERNAME COMPANY EMAIL PHONE
Table: Dispatchers.
USERNAME DISPATCH_CLIENT
I need to get all the rows in the Users table that have a specific company name
I also need to get all the rows in the Users table where the USERNAME and DISPATCH_CLIENT fields in the Dispatch table match the USERNAME AND COMPANY field in Users table.
I have looked at some questions on here using EXISTS, but it either didn't work in my situation or i'm not smart enough to understand it.
This is what I have at the moment.
SELECT *
FROM Users
WHERE Users.COMPANY = '" . $company . "'
AND EXISTS
(SELECT USERNAME
FROM Dispatchers WHERE DISPATCH_CLIENT = '" . $company . "')";
Also tried doing it this way but no records are returned:
SELECT
*
FROM
Users
INNER JOIN
Dispatchers
ON Dispatchers.USERNAME = Users.USERNAME
AND Dispatchers.DISPATCH_CLIENT = Users.COMPANY
WHERE
Users.COMPANY = '" . $company . "'"

Answer 1

Try this
SELECT *
FROM Users
WHERE Users.COMPANY = '" . $company . "'
OR Users.USERNAME IN
(SELECT USERNAME
FROM Dispatchers WHERE DISPATCH_CLIENT = '" . $company . "')";

Answer 2

I think you missed the join condition in "exists" phase. Please try this.
SELECT *
FROM Users
WHERE Users.COMPANY = '" . $company . "'
AND EXISTS
(SELECT USERNAME
FROM Dispatchers
WHERE Dispatchers.DISPATCH_CLIENT = Users.COMPANY
and Users.USERNAME = Dispatchers.USERNAME)