Utilize the input text as a context reference, choose the right relationship between Costco and retail from the options. Options: product/material produced, manufacturer, distributed by, industry, position held, original broadcaster, owned by, founded by, distribution format, headquarters location, stock exchange, currency, parent organization, chief executive officer, director/manager, owner of, operator, member of, employer, chairperson, platform, subsidiary, legal form, publisher, developer, brand, business division, location of formation, creator.

Though Sam's Club has roughly as many stores as rival Costco Wholesale ( NASDAQ:COST ) , its sales are only about half that of the leading warehouse retail brand.

Answer: industry