SQLite Forum

Removing not null constraint doesn't behave correctly
If you revise the title of this thread to indicate that this is a bug, Richard Hipp will likely notice it and read far enough to see that something is in fact awry, either with the library itself or the documentation that led you to believe it should work. This forum is where bugs are reported, by project convention.

My initial response to your post was to say that "behave correctly" does not apply because modifying sqlite_master was **not** supported until quite recently. If I recall correctly, it was positively warned against. It was only after I noticed your claim in a comment that you were following a procedure in the docs that I went to read about this newly advised approach to schema altering.

I would think that where sqlite_master (or sqlite_schema lately) modification is recommended there would be some clearly delineated boundary between what will work and what may not. There is already a caution about changes that invalidate table data on disk. Something similar regarding table and column constraints may be needed. Or it might be documented that changing those will not take effect until certain things happen, such as reopening the database.