Another Between Date question

Vague question are you using regular PHP or carbon date, if carbon have you looked at the documentation for carbon they have a wealth of examples.

Sorry, regular PHP/Laravel

The problem with that query isn't the where between clause, it's that you're trying to select from two tables without specifying how to join them.

I assume employees have a company_id on them, so the resulting SQL should look like this:

SELECT employee_id FROM employees
  JOIN company ON employees.company_id = company.id
  WHERE employees.birthdate BETWEEN company.beginDate and company.endDate

With query builder you could do it like this:

$employee_ids = DB::table('employees')
  ->leftJoin('company', 'employees.company_id', '=', 'company.id')
  ->whereBetween('employees.birthdate', ['company.startDate', 'company.endDate'])
  ->pluck('employee_id');