sharing Codes in sql database

i have table location_stock with column product_id,product_name,product_code,product_scancode

dataa are like follows

1 ,test,0001,0001

2,test2,0002,0002

3,test3,0003,0003

problem is product_code number 0001,is sold always and product_code 0002,now i came to see that product_code 0003 when i came to select has changed the code itself to 0001 once i select 0001 and 0003 ,0001 and quantity to 2 ,help me to solve this