Mysql concat

 SELECT lower(concat(first_name,'.',last_name,',com')) as Domain FROM `employees`

Domain
john.doe,com
jane.smith,com

MYSQL quering multiple tables and inner join

 

SELECT t1.employee_id, t1.first_name, t2.order_id,t2.order_date FROM employees AS t1 INNER JOIN orders AS t2 ON t2.employee_id = t1.employee_id

select t1.employee_id,t1.first_name,t2.product_name,t3.order_date,t3.employee_id from employees as t1,products as t2,orders as t3 where t3.order_id=t1.employee_id

SELECT t1.employee_id, t1.first_name, t2.product_name, t3.order_date, t3.employee_id FROM employees AS t1 INNER JOIN orders AS t3 ON t3.employee_id = t1.employee_id INNER JOIN products AS t2 ON t2.product_id = t3.product_id

mysqltutorial

 https://www.mysqltutorial.org/