sql question(s)

I need to select a range of number from a table and display them via html. I've got everything working but the select. When I use: select * from tableA where number >= X; I get those >= X . However when I try to grab a range say >=X <=Y I get the entire table. I am sure there's just a simple error here but I cannot figure it out. This same data is updated every evening. I want to keep at least 4 nights of data search able. Currently I am updating every night which wipes out the previous nights data. How would I go about keeping table data for a few days? thanks, Michael