Table:
0
A
B
C
1
document type code
document type description
reference document types
2
CD
b
3
Paper
u
4
Hard Drive
f

Questions and formulas:
Question: What document type codes do we have?
Formula: UNIQUE(A1)
Formula2: UNIQUE(A2:A4)
Level: easy
Question: What is the description of document type 'Paper'?
Formula: UNIQUE(CHOOSECOLS(FILTER(A1:C1,A1="paper"),2))
Formula2: UNIQUE(CHOOSECOLS(FILTER(A2:C4,A2:A4="paper"),2))
Level: medium