SQL Server 2017

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declare @t1 table (Col1 smallint, Col2 char(2), Col3 smallint);

insert @t1 values

(0, 'AA', 1),

(0, 'AB', 2),

(1, 'AC', 1);

declare @t2 table (Col1 smallint, Col2 char(2), Col3 smallint);

insert @t2 values

(0, 'AA', 1),

(0, 'AB', 2),

(0, 'AC', 2);

with cte as (

select *, 't1' as tbl from @t1

union all

select *, 't2' as tbl from @t2

)

select Col1, Col2, Col3, min(tbl) as tbl

from cte

group by Col1, Col2, Col3

order by Col1, Col2, Col3;