Retrieve a record from mysql in golang using database/sql

I'm trying to retrieve a record from mysql table and marshal it to json.
But i gotted the error that says : ".\main.go:67: no new variables on left sife of :="
I'm new in Golang Plz! help me to solve out this error!
My Code is :

func GetUser(w http.ResponseWriter, r *http.Request) {
urlParams   := mux.Vars(r)
id       := urlParams["id"]
ReadUser := User{}
con, err := sql.Open("mysql", "root:YES@/social_network?charset=utf8")
err := con.QueryRow("select * from users where user_id=?",id).Scan(&ReadUser.ID, &ReadUser.Name, &ReadUser.First, &ReadUser.Last, &ReadUser.Email )
switch {
case err == sql.ErrNoRows:
fmt.Fprintf(w,"No such user")
case err != nil:
log.Fatal(err)
default:
output, _ := json.Marshal(ReadUser)
fmt.Fprintf(w,string(output))
}
}

and Routes in main:

func main() {
gorillaRoute := mux.NewRouter()
gorillaRoute.HandleFunc("/api/user/create", CreateUser)
gorillaRoute.HandleFunc("/api/user/read/:id", GetUser)
http.Handle("/", gorillaRoute)
http.ListenAndServe(":8080", nil)
}

Here is my new Code , but again not able to get record from database table, plz help me to figure out the error OR what things i do wrong?
package main

import (
"database/sql"
"encoding/json"
"fmt"
"log"
"net/http"
_ "github.com/go-sql-driver/mysql"
"github.com/gorilla/mux"
)
type API struct {
Message string "json:message"
}
type User struct {
ID    int    "json:id"
Name  string "json:username"
Email string "json:email"
First string "json:first"
Last  string "json:last"
}
func Hello(w http.ResponseWriter, r *http.Request) {
// urlParams := mux.Vars(r)
// name := urlParams["user"]
HelloMessage := "User Creation page"
message := API{HelloMessage}
output, err := json.Marshal(message)
if err != nil {
fmt.Println("Something went wrong!")
}
fmt.Fprintf(w, string(output))
}
//POST A USER INTO DB
func CreateUser(w http.ResponseWriter, r *http.Request) {
NewUser := User{}
NewUser.Name = r.FormValue("user")
NewUser.Email = r.FormValue("email")
NewUser.First = r.FormValue("first")
NewUser.Last = r.FormValue("last")
output, err := json.Marshal(NewUser)
fmt.Println(string(output))
if err != nil {
fmt.Println("Something went wrong!")
}
con, err := sql.Open("mysql", "root:YES@/social_network?charset=utf8")
sqlQuery := "INSERT INTO users set user_nickname='" + NewUser.Name + "', user_first='" + NewUser.First + "', user_last='" + NewUser.Last + "', user_email='" + NewUser.Email + "'"
q, err := con.Exec(sqlQuery)
if err != nil {
fmt.Println(err)
}
fmt.Println(q)
}
//GET USERS FROM DB
func GetUsers(w http.ResponseWriter, r *http.Request) {
db, err := sql.Open("mysql", "root:YES@/social_network?charset=utf8")
if err != nil {
panic(err)
}
err = db.Ping()
if err != nil {
panic(err)
}
defer db.Close()
rows, err := db.Query("select * from users ")
if err != nil {
log.Fatal(err)
}
defer rows.Close()
var rowBuf, _ = rows.Columns()
var cols = make([]string, len(rowBuf))
copy(cols, rowBuf)
fmt.Println(rowBuf)
var vals = make([]interface{}, len(rowBuf))
for i, _ := range rowBuf {
vals[i] = &rowBuf[i]
}
for rows.Next() {
err := rows.Scan(vals...)
if err != nil {
log.Fatal(err)
}
var m = map[string]interface{}{}
for i, col := range cols {
m[col] = vals[i]
}
obj, _ := json.Marshal(m)
//
fmt.Fprintf(w, string(obj))
}
err = rows.Err()
if err != nil {
log.Fatal(err)
}
}
func GetUser(w http.ResponseWriter, r *http.Request) {
urlParams := mux.Vars(r)
id := urlParams["id"]
ReadUser := User{}
db, err := sql.Open("mysql", "root:YES@/social_network?charset=utf8")
stmt := db.QueryRow("select * from users where id = ?", id)
if err != nil {
log.Fatal(err)
}
err = stmt.Scan(&ReadUser.ID, &ReadUser.Name, &ReadUser.First, &ReadUser.Last, &ReadUser.Email)
if err != nil {
log.Fatal(err)
}
result, err := json.Marshal(ReadUser)
fmt.Fprintf(w, string(result))
}
func main() {
gorillaRoute := mux.NewRouter()
gorillaRoute.HandleFunc("/api/user/create", CreateUser)
gorillaRoute.HandleFunc("/api/user/read", GetUsers)
gorillaRoute.HandleFunc("/api/user/:id", GetUser)
http.Handle("/", gorillaRoute)
http.ListenAndServe(":8080", nil)
}

Remove the colon : from err := as you are assigning a new value to existing variable.