a	d	s
1	2013-02-21	first
2	2013-02-21	second
a	d	s
0	2010-01-05	NULL
0	2010-03-05	NULL
1	2010-02-05	NULL
a	d	s
1	2010-02-05	first
2	2013-02-21	second
a	d	s
1	2010-03-05	first
2	2010-03-05	second
a	d	s
1	2010-04-05	first
2	2010-03-05	second