MariaDB 10.3

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create table test (k1 int, k2 int, k3 int, data varchar(1))
insert into test values 
(  1 ,   1  ,   1  ,   'a'   ),
(  1 ,   1  ,   2  ,   'b'   ),
(  1 ,   2  ,   1  ,   'c'   ),
(  1 ,   2  ,   2  ,   'd'   ),
(  2 ,   1  ,   1  ,   'e'   ),
(  2 ,   1  ,   2  ,   'f'   ),
(  2 ,   2  ,   1  ,   'g'   ),
(  2 ,   2  ,   2  ,   'h'   )

Records: 8  Duplicates: 0  Warnings: 0


select * from (select t.*, row_number() over (partition by k1, k2 order by rand()
) as rn from test t ) tt where rn = 1 order by k1, k2, k3


k1
k2
k3
data
rn


1
1
2
b
1

1
2
2
d
1

2
1
2
f
1

2
2
1
g
1