求助一个 panic: runtime error: invalid memory address or nil pointer dereference 问题

报错

panic: runtime error: invalid memory address or nil pointer dereference

代码

import (
“database/sql”
_ “github.com/go-sql-driver/mysql”
)

var (
db *sql.DB
)
func init() {
db, err := sql.Open("mysql", "root:root@tcp(localhost:3306)/test?charset=utf8")
if err != nil {
panic(err.Error()) // Just for example purpose. You should use proper error handling instead of panic
}

defer db.Close()

}