我的代碼如下：package mainimport (  "database/sql"  "fmt"  _ "github.com/mattn/go-sqlite3"  "log")var db *sql.DBfunc main() {  fmt.Println("Starting test ...")  db, err := sql.Open("sqlite3", "./data.db")  checkErr(err)  err = db.Ping()  checkErr(err)  fmt.Println(getNames())}func checkErr(err error) {  if err != nil {    log.Fatal(err)  }}func getNames() []string {  query := `select name from places`  rows, err := db.Query(query)  checkErr(err)  defer rows.Close()  var names []string  for rows.Next() {    var name string    rows.Scan(&name)    names = append(names, name)  }  return names}我遇到了這個問題，但這種方法對我不起作用。我正在使用 sqlite3 進行存儲。我的目標很簡單。在所有函數(shù)之間共享 db 處理程序。構建和運行時出現(xiàn)以下錯誤。Starting test ...panic: runtime error: invalid memory address or nil pointer dereference[signal 0xb code=0x1 addr=0x0 pc=0x411fc6e]goroutine 1 [running]:database/sql.(*DB).conn(0x0, 0x0, 0x0, 0x0)    /usr/local/Cellar/go/1.4.2/libexec/src/database/sql/sql.go:634   +0x7aedatabase/sql.(*DB).query(0x0, 0x421cb10, 0x17, 0x0, 0x0, 0x0, 0x1, 0x0, 0x0)    /usr/local/Cellar/go/1.4.2/libexec/src/database/sql/sql.go:933 +0x43database/sql.(*DB).Query(0x0, 0x421cb10, 0x17, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0)    /usr/local/Cellar/go/1.4.2/libexec/src/database/sql/sql.go:924 +0xa6main.getNames(0x0, 0x0, 0x0)    /Users/kdys/Code/go/src/test/main.go:32 +0x94main.main()    /Users/kdys/Code/go/src/test/main.go:21 +0x188goroutine 5 [chan receive]:database/sql.(*DB).connectionOpener(0xc20802e000)    /usr/local/Cellar/go/1.4.2/libexec/src/database/sql/sql.go:589 +0x4ccreated by database/sql.Open    /usr/local/Cellar/go/1.4.2/libexec/src/database/sql/sql.go:452 +0x31cgoroutine 17 [syscall, locked to thread]:runtime.goexit()    /usr/local/Cellar/go/1.4.2/libexec/src/runtime/asm_amd64.s:2232 +0x1我在這里做錯了什么？