I'm using db2 version 9.7* and it seems impossible to make a NOT NULL column nullable in any straightforward way.
Unfortunately the solution of using a more developer friendly database is not available. Basically, in MySQL speak, I want to do something like this (where MY_COLUMN used to be VARCHAR(200) NOT NULL) :
ALTER TABLE MY_TABLE MODIFY COLUMN MY_COLUMN VARCHAR(200);
My final query ended up something like this:
ALTER TABLE MY_TABLE DATA CAPTURE NONE;
ALTER TABLE MY_TABLE ALTER MY_COLUMN DROP NOT NULL;
ALTER TABLE MY_TABLE DATA CAPTURE CHANGES;