Louis Armstrong แสดงกี่ปี?ไม่จำเป็นต้องใช้ตารางทั้งหมด
How many years was Louis Armstrong performing?It is not neccessary to use all the tables.
 table_name_51:  (year [ VARCHAR ] performer_s_ [ VARCHAR) ]
SELECT COUNT(year) FROM table_name_51 WHERE performer_s_ = "louis armstrong"