Why is China Southern Airlines a plane of Chongqing Airlines?

China Southern Airlines is an aircraft of Chongqing Airlines, because Chongqing Airlines is a holding subsidiary of China Southern Airlines. There is a cooperative relationship of code sharing between China Southern Airlines and Chongqing Airlines. China Southern Airlines put flight numbers on some flights of Chongqing Airlines, and Chongqing Airlines put flight numbers on some flights of China Southern Airlines. In this way, passengers of the two companies can purchase flights of another company through the reservation system of either company, enjoying more choices and convenience. So buy tickets on China Southern Airlines APP, and both China Southern Airlines and Chongqing Airlines can buy them.