Would a FULL OUTER JOIN help?

I changed your sample data to get some results.

-- sample data

DECLARE @table1 TABLE (id int identity, content int NOT NULL, primary key(id, content));

DECLARE @table2 TABLE (id int identity, content int NOT NULL, primary key(id, content));

INSERT @table1(content) VALUES (12), (15), (20);

INSERT @table2(content) VALUES (13), (15), (20);

--DELETE TOP(1) FROM @table1;

--DELETE TOP(1) FROM @table2;

--solution

(

SELECT id, content FROM @table1

EXCEPT

SELECT id, content FROM @table2

)

UNION ALL

(

SELECT id, content FROM @table2

EXCEPT

SELECT id, content FROM @table1

);

SELECT ISNULL( t1.id, t2.id) AS id,

ISNULL( t1.content, t2.content) AS content

FROM @table1 t1

FULL OUTER

JOIN @table2 t2 ON t1.id = t2.id AND t1.content = t2.content

WHERE t1.id IS NULL

OR t2.id IS NULL;

Or maybe using HAVING:

SELECT *

FROM (

SELECT id, content FROM @table1

UNION ALL

SELECT id, content FROM @table2

) x

GROUP BY id, content

HAVING COUNT(*) = 1;