optimization in C

This solution isn't good when there are +10000 tuples in the table, it's
slowly...
anybody can help me ? :

string = "SELECT service, noeud, rubrique FROM table" ;res = PQexec( conn, string.data() ) ;if ( (! res) || (status =
PQresultStatus(res ) != PGRES_TUPLES_OK) ){    cerr << _ERROR << "Problem SELECT ! " << endl ;    cerr << _ERROR <<
"Error: " << PQresStatus( status ) << endl ;    cerr << _ERROR << "Error : " << PQresultErrorMessage( res ) << endl ;
PQclear( res ) ;}else{    for (int m=0; m < PQntuples( res ); m++)    {        service = PQgetvalue( resultat1, m, 0 )
;       noeud = PQgetvalue( resultat1, m, 1 ) ;        rubrique = PQgetvalue( resultat1, m, 2 ) ;
 
        commande = "SELECT SUM(date) FROM table WHERE service='" + service +
"' AND noeud='" + noeud + "' AND rubrique='"+ rubrique + "'" ;        res1 = PQexec( conn, string.data() ) ;        if
((! res1) || (status = PQresultStatus( res1 ) != PGRES_TUPLES_OK)
 
)        {            cerr << _ERROR << "Problem SUM ! " << endl ;            cerr << _ERROR << "Error : " <<
PQresStatus(status ) << endl ;            cerr << _ERROR << "Error : " << PQresultErrorMessage( res1 ) << endl
 
;            PQclear( res1 ) ;        }        else        {            cout << _TRACE << "SUM ok." << endl ;
PQclear( res1 ) ;        }    }    PQclear( res ) ;}
 

Thanks. jerome.