SQL Server 2016

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create table t(col varchar(100));

insert into t values('A'),('B'),('C');
3 rows affected

select * from t

col

A

B

C

select i1.col, i2.col, i3.col
from t i1 join
     t i2
     on i2.col not in (i1.col) join
     t i3
     on i3.col not in (i1.col, i2.col)

col
col
col

A
C
B

A
B
C

B
C
A

B
A
C

C
B
A

C
A
B

select i1.col+i2.col+i3.col as output
from t i1 join
     t i2
     on i2.col not in (i1.col) join
     t i3
     on i3.col not in (i1.col, i2.col)

output

ACB

ABC

BCA

BAC

CBA

CAB

select distinct t2.c+t3.col from 
(select i1.col+i2.col as c
from t i1 cross join
     t i2
     ) as t2 cross join
     t t3
    
(No column name)

AAA

AAB

AAC

ABA

ABB

ABC

ACA

ACB

ACC

BAA

BAB

BAC

BBA

BBB

BBC

BCA

BCB

BCC

CAA

CAB

CAC

CBA

CBB

CBC

CCA

CCB

CCC