Hi,
you want to directly access the database.
Well, in a not anonymous survey you can merge "lime_survey_123456" and "lime_token_123456" by the token.
And if "submitdate" is NULL the survey was not completed.
In an anonymous survey the token column is not filled. This is obvious.
In the GUI the table of answers automatically merges these two tables.
If you only want to know who answered, who did not you may use the table "lime_token_123456".
Here you find all data if the participant and the field "completed". Either "N" or date of completion.
Joffm