casestament

i have an issue in case statement  question i have one table t there are two column firest one item and second size item would be like

item             size

a                1

b                1

c               0

d              1

e              0

when i write a query  and pass yes in where condition then select all 1 in size column or pass no then select 0 and pass all then show all 0 and 1