Will the Where condition be better than the JOIN table condition?

Dear experts,

I've question with mysql query.  I want to process an online order which users will input the item number and the quantity that they wish to buy.

Will it be better that I store the item number and quantity into a temporary table and do a JOIN with the item number (item numbers are unique number) in my item table or I can select the columns that I need from item table and place all the item numbers provided by users in the where condition of a query?

User's input can be ranged from a single row to few thousand rows(maybe 10K on rare occasions).

Thanks