-- no modifiers
A	2
B	3
C	\N
D	1
1	D
2	A
3	B
\N	C
A	2
B	3
C	\N
D	1
1	D
2	A
3	B
\N	C
-- with ASC/DESC modifiers
A	2
B	3
C	\N
D	1
D	1
C	\N
B	3
A	2
A	2
B	3
C	\N
D	1
D	1
C	\N
B	3
A	2
-- with NULLS FIRST/LAST modifiers
\N	C
1	D
2	A
3	B
1	D
2	A
3	B
\N	C
\N	C
1	D
2	A
3	B
1	D
2	A
3	B
\N	C
-- what happens if some column "all" already exists?
B	3	10
D	1	20
A	2	30
C	\N	40
B	3	10
D	1	20
A	2	30
C	\N	40
D	1
A	2
B	3
C	\N
D	1
A	2
B	3
C	\N
A 2
B 3
D 1
\N
A 2
B 3
D 1
\N
B	3	10
D	1	20
A	2	30
C	\N	40
B	3	10
D	1	20
A	2	30
C	\N	40