SELECT @sum:=SUM(`int1` + `int1_key` + `int1_unique`
               + `int2` + `int2_key` + `int2_unique`) 
         AS TotalSum 
         FROM t1;

# Get some diagnostics if sum is non-zero
if (`SELECT @sum`)
{
    # Get sum of consistent rows (should be 0)
    SELECT SUM(`int1` + `int1_key` + `int1_unique` + `int2` + `int2_key` + `int2_unique`) FROM t1 where `is_consistent` = 1;

    # Get sum of inconsistent rows (should be non-0 if the total sum is to be non-0)
    SELECT SUM(`int1` + `int1_key` + `int1_unique` + `int2` + `int2_key` + `int2_unique`) FROM t1 where `is_consistent` = 0;

    # Get number of inconsistent rows
    SELECT COUNT(*) FROM t1 WHERE `is_consistent` = 0;

    # See if there is a single row which is the culprit
    SELECT * FROM t1 WHERE `int1` + `int1_key` + `int1_unique` + `int2` + `int2_key` + `int2_unique` = @sum;

    SELECT * FROM t1 WHERE `int1` + `int1_key` + `int1_unique` + `int2` + `int2_key` + `int2_unique` = -@sum;
}