display the emails of the employees who have no commission percentage and salary within the range 7000 to 12000 and works in that department which number is 50.
SELECT email FROM employees WHERE commission_pct   =   "null" AND salary BETWEEN 7000 AND 12000 AND department_id  =  50
no commission percentage refers to commission_pct IS NULL; salary within the range 7000 to 12000 refers to salary BETWEEN 7000 AND 12000; works in department number 50 refers to department_id = 50;