不支持的扫描，存储驱动程序。值类型

Question

I want to select fild in database and return 3 vriables with golang, this is my actual code :

func db_tabela_select(cliente string) (id string, cod1 string, cod2 string, cod3 string) {

    db, err := sql.Open("mysql", mysql_login)
    if err != nil {
        log.Fatal(err)
    }
    defer db.Close()

    err = db.Ping()
    if err != nil {
        log.Fatal(err)
    }


    var Saldo, grup1, grup2, grup3, timestamp, user_agent string

    err = db.QueryRow(fmt.Sprintf("select * from db_tabela WHERE `cliente`='%s' LIMIT 1;", string(cliente) )).Scan(
        &id, &cliente, &Saldo, &cod1, &cod2, &cod3, &grup1, &grup2, &grup3, &user_agent, &timestamp)
    if err != nil {
        fmt.Println(err)
    } else {
        log.Printf("cod results : ", cod1, cod2, cod3)
    }


    return id, cod1, cod2, cod3
}

return me this error, and i don't understend where is my mistake:

sql: Scan error on column index 2: unsupported Scan, storing driver.Value type <
nil> into type *string