I had a problem, and the method Mike advised worked partly, I had an error Dublicate Column name = '0', and changed the syntax of your query as this`
$tQ = "INSERT INTO names (name_id, surname_id, sum, sum2, sum3,sum4,sum5)
SELECT '$name', '$surname', '$sum', '$sum2', '$sum3','$sum4','$sum5'
FROM DUAL
WHERE NOT EXISTS (
SELECT sum FROM names WHERE name_id = '$name'
AND surname_id = '$surname') LIMIT 1;";
The problem was with column names. sum3 was equal to sum4 and mysql throwed dublicate column names, and I wrote the code in this syntax and it worked perfectly,