Hi and thanks to everyone for the interest. Keith, I tried you suggestion which ran without a problem from the CLI but throws an error when run from SQLite Studio and also when I tried to run it from the Python interface. Also the output when run from the CLI was suspect, possibly for one of the reasons you described. In the mean time I have followed Larry's advise and gone back to the documentation. My latest attempt at this query is: sqlite> UPDATE activity_overview ...> SET 'D3' = 1 ...> FROM activity_overview INNER JOIN query_projects ON activity_overview."Project ID"= query_projects."Project ID" ...> WHERE activity_overview."Early Start" < query_projects."Planned Start"; Error: ambiguous column name: activity_overview.Early Start sqlite> Which gets further but unfortunately still throws the above error. I have followed the flow chart documented in 'SQL As Understood By SQLite - Update' but I am obviously still missing something. At the risk of testing your patience, can anyone give me a further pointer? Atb JZ