How do you keep display only fields from being inserted into tables?

Question

Morning I have a problem where I am displaying a couple fields on a screen and they are tring to insert in to a table.
I am running Apex 4.1 on 11Gr2, i am building a set of screens, on the first one the user inputs a subject ID, that branchs to a second screen that uses the subject id to do a lookup for a couple fields for display. there are a couple field the user feels in and a row is inserted in to a differnet table. But Apex is tring to insert the lookup fields in to the second table when I really only need the subject ID.
How can I tell Apex which fields to use in the insert and which not to try to uses. I see in the debug it is getting all the screen fields in the inserty statement.
Thanks

Answer 1

In the insert process, take the cols out which you don't want to insert, say,
insert into tbl (col1, col2, ....) value (p1, p2, ...)
=>
insert into tbl (col1, col5, ....) values (p1, p5, ...)