USER			
uid	name	country	sex
1	'andreas'	'greece'	'male'
2	'aris'	'greece'	'male'
3	'anna'	'greece'	'female'
4	'dimitris'	'greece'	'male'
5	'katerina'	'greece'	'female'
6	'kostas'	'greece'	'male'
7	'maria'	'greece'	'female'
8	'panos'	'greece'	'male'
9	'petros'	'greece'	'male'

GROUP		
group-name	user-id	date-of-joining
'book-lovers'	1	'2016-12-10'
'book-lovers'	2	'2016-05-10'
'enigma'	1	'2016-01-20'
'enigma'	2	'2016-03-25'
'book-lovers'	4	'2016-12-25'
'puzzlers'	3	'2016-01-20'
'puzzlers'	5	'2016-03-25'
'the hive'	3	'2016-12-10'
'the hive'	5	'2016-12-11'
'enigma'	6	'2016-12-12'
'enigma'	7	'2016-12-13'
'the hive'	6	'2016-12-14'
'the hive'	7	'2016-12-15'

POST			
post-id	user-id	date-of-post	time-of-post
1	1	'2016-12-10'	'10:00:01'
2	2	'2016-05-10'	'10:40:01'
3	3	'2015-10-10'	'00:00:01'
4	5	'2015-03-10'	'05:00:01'
5	6	'2014-08-10'	'10:00:01'
6	7	'2014-01-10'	'09:30:10'
7	4	'2016-12-25'	'09:00:19'
8	1	'2016-12-26'	'08:30:28'
9	2	'2016-12-27'	'08:00:37'

POST-CONTENT	
post-id	keyword
1	'hi'
1	'good'
1	'test'
2	'hi'
2	'good'
2	'test'
3	'dog'
3	'cat'
4	'car'
4	'bike'
5	'netflix'
5	'ebay'
5	'amazon'
6	'netflix'
6	'ebay'
6	'amazon'
7	'cs'
7	'university'
8	'blue'
8	'shadow'
8	'running'
9	'capacity'
9	'power'
9	'replacement'