Table:
0
A
B
C
D
E
F
G
1
staff id
project id
role code
date from
date to
other details
project staff
2
0.0
2
leader
1981-10-04 22:44:50
1985-05-30 22:26:30
3
674810.0
5
leader
2003-04-19 15:06:20
2010-12-08 11:55:36
4
779.0
2
researcher
1981-10-09 21:32:53
2004-12-16 13:03:36
5
6572.0
4
researcher
1983-02-07 17:55:59
2004-07-28 03:11:47
6
5353407.0
15
leader
2004-11-01 23:52:38
1988-03-04 19:30:05
7
5137097.0
7
researcher
1991-01-11 16:57:50
1993-06-09 12:44:28
8
29.0
9
researcher
2005-01-13 11:49:48
1973-07-19 04:51:26
9
3.0
8
researcher
1970-03-25 06:18:11
1985-12-05 12:00:58
10
3100031.0
11
researcher
1972-01-17 19:42:16
2016-03-15 00:33:18
11
49698449.0
1
leader
1970-04-06 15:50:21
1983-03-19 16:06:31
12
45.0
11
researcher
2000-08-28 11:49:17
2007-02-02 17:26:02
13
37.0
5
researcher
1989-04-24 23:51:54
2002-03-19 18:00:36
14
6065505.0
3
leader
1999-10-21 22:07:15
2008-09-25 20:06:28
15
56.0
1
leader
1970-01-02 15:35:05
1985-09-22 09:06:08
16
13739108.0
2
researcher
1973-12-12 11:46:28
1971-07-19 22:49:05

Questions and formulas:
Question: Are there any role code results for researchers? 
Formula: FILTER(A1:G1, C1="researcher")
Formula2: FILTER(A2:G16, C2:C16="researcher")
Level: easy
Question: All staff ids and role codes.
Formula: UNIQUE(HSTACK(A1,C1))
Formula2: UNIQUE(HSTACK(A2:A16,C2:C16))
Level: easy
Question: Show staff and their roles between 2003-04-19 15:06:20 and 2016-03-15 00:33:18.
Formula: LET(query1,FILTER(A1:G1,(D1>=Date(2003, 4, 19))*(E1<=Date(2016, 3, 15))),UNIQUE(CHOOSECOLS(query1,1,3)))
Formula2: LET(query1,FILTER(A2:G16,(D2:D16>=Date(2003, 4, 19))*(E2:E16<=Date(2016, 3, 15))),UNIQUE(CHOOSECOLS(query1,1,3)))
Level: hard
Question: What is the most common role code?
Formula: TAKE(SORT(SUMMARIZE(C1,COUNTX(C1)), 2, -1), 1)
Formula2: TAKE(SORT(SUMMARIZE(C2:C16,COUNTX(C2:C16)), 2, -1), 1)
Level: hard
Question: Any researcher in role code?
Formula: FILTER(A1:G1, C1="researcher")
Formula2: FILTER(A2:G16, C2:C16="researcher")
Level: easy
Question: The staff ids and role codes.
Formula: UNIQUE(HSTACK(A1,C1))
Formula2: UNIQUE(HSTACK(A2:A16,C2:C16))
Level: easy
Question: The staff and their roles from 2003-04-19 15:06:20 to 2016-03-15 00:33:18.
Formula: LET(query1,FILTER(A1:G1,(D1>=Date(2003, 4, 19))*(D1<Date(2016, 3, 15))),UNIQUE(CHOOSECOLS(query1,1,3)))
Formula2: LET(query1,FILTER(A2:G16,(D2:D16>=Date(2003, 4, 19))*(D2:D16<Date(2016, 3, 15))),UNIQUE(CHOOSECOLS(query1,1,3)))
Level: hard
Question: What role code does the most staff have?
Formula: TAKE(SORT(SUMMARIZE(C1,SUMX(A1)), 2, -1), 1)
Formula2: TAKE(SORT(SUMMARIZE(C2:C16,SUMX(A2:A16)), 2, -1), 1)
Level: hard