A quick update for those interested:

The second part of the column header in the survey responses table is indeed the group ID (gid in the ls_questions table).

The third part either is the question id (qid in the ls_questions table), when the question has no parent_qid. I assume this is the case for full text questions for example, but maybe any question that is not an array and that doesn't have sub-questions.

For those questions that do have multiple sub-questions (e.g. array question), the last part consists of the parent_qid and the "title" (from the ls_questions table). I assume this last bit is the identifier of the sub-question.

Happy to be corrected by anyone in the know, these are just guesses based on the data in my database.

You might check the old and new database structures here:
manual.limesurvey.org/LimeSurvey_1.8_dat...layout_documentation

There was a newer diagram posted in the Spanish section.
See attachment here:
www.limesurvey.org/forum/spanish-forum/1...ntidad-de-limesurvey

About "Response table" : i think it's better to use a 'false' table export with ngood header.

UYou can use export as json or do your own export : framagit.org/SondagePro-LimeSurvey-plugi.../jsonPivotWriter.php for an example