Use Sum in MySQL Database in Golang

package main

import (
    "database/sql"
    "fmt"
)

func ConnectDB() (db *sql.DB, err error) {
    dbDriver := "mysql"
    dbUser := "root"
    dbPass := "nilpointer.net"
    dbName := "nilpointer_db"
    db, err = sql.Open(dbDriver, dbUser+":"+dbPass+"@/"+dbName)
    return
}

func main() {

    db, err := ConnectDB()
    if err != nil {
        fmt.Println(err)
    } else {
        rows, err2 := db.Query("select sum(quantity) as sum_quantities from mobile")
        if err2 != nil {
            fmt.Println(err2)
        } else {
            var sum_quantities int64
            for rows.Next() {
                rows.Scan(&sum_quantities)
            }
            fmt.Println("sum: ", sum_quantities)
        }
    }
}