I would approach it by forming a basic query like this to get the user id:
select u.user_id from tbl_user u
then, assuming we get the user id data in $users variable i would run the following query in a foreach ($users as $user) loop:
select u.user_id, u.user_name, u.user_email, u.user_country, q.survey_question, a.answers from tbl_user u
inner join tbl_survey s on u.user_id = s.user_id
inner join tbl_answers a on a.answer_id = s.answer_id
inner join tbl_questions q on q.question_id = s.question_id
where u.user_id = %user
order by u.user_id, q.survey_id'
Finally, parse the query into a user-question array.
Exporting to excel question was already answered by Baba in https://stackoverflow.com/a/10424955/3986395 and i will share his answer here:
header("Content-Disposition: attachment; filename=\"demo.xls\"");
header("Content-Type: application/vnd.ms-excel;");
header("Pragma: no-cache");
header("Expires: 0");
$out = fopen("php://output", 'w');
foreach ($array as $data)
{
fputcsv($out, $data,"\t");
}
fclose($out);
Finally, if you have millions of users you might not want to run the query in a foreach loop and instead write a combined query to get all user data. This query would give you user_id-answer records and you would need additional processing logic in php to merge the data into required array
select u.user_id, u.user_name, u.user_email, u.user_country, q.survey_question, a.answers from tbl_user u
inner join tbl_survey s on u.user_id = s.user_id
inner join tbl_answers a on a.answer_id = s.answer_id
inner join tbl_questions q on q.question_id = s.question_id
where ..
order by u.user_id, q.survey_id
