我在下面的代碼中給出了未定義的錯誤sql.Open。不確定如何解決此錯誤。任何幫助解決此錯誤？79:16 sql.Open 未定義（類型字符串沒有字段或方法打開）進程退出，代碼：2 信號：假package mainimport (    "database/sql"    "fmt"    "io/ioutil"    "log"    "os"    "path/filepath"    "runtime"    "sort"    "strings"    _ "github.com/go-sql-driver/mysql")const (    username = ""    password = ""    hostname = ""    dbname   = "")type Server struct {    ID          int    Servername  string    IP          sql.NullString `json:"ip"`    OS          sql.NullString `json:"os"`}func dsn(dbName string) string {    return fmt.Sprintf("%s:%s@tcp(%s)/%s", username, password, hostname, dbName)}func RemoveDuplicates(xs *[]string) {    found := make(map[string]bool)    j := 0    for i, x := range *xs {        if !found[x] {            found[x] = true            (*xs)[j] = (*xs)[i]            j++        }    }    *xs = (*xs)[:j]}func main() {    var TEMPDIR = os.Getenv("HOME")    if runtime.GOOS == "windows" {        TEMPDIR = "c:\\temp"    }    filename := filepath.FromSlash(TEMPDIR + "/a.txt")    content, err := ioutil.ReadFile(filename)    if err != nil {        log.Fatal(err)    }    text := string(content)    fmt.Println(text)    w := strings.Fields(text)    RemoveDuplicates(&w)    sort.Strings(w)    j := strings.Join(w, "','")    result := "('" + j + "')"    sql := "SELECT * FROM servers where servername in " + result    fmt.Println("sql: ", sql)    db, err := sql.Open("mysql", dbname)    if err != nil {        log.Printf("Error %s when opening DB\n", err)        return    }    defer db.Close()    log.Printf("Connected to DB\n")}謝謝