//로그인라우터
router.post('/login',(req,res)=>{
    let id = req.body.userId
    let pw = req.body.userPw
    let loginSql = 'SELECT USER_ID, USER_PW, USER_NICK, USER_NAME, USER_LEVEL FROM TB_USER WHERE USER_ID =?'
    conn.connect()

    conn.query(loginSql,[id],(err,result)=>{
        if(err){
            console.log('쿼리문 에러')
        }
        else{
            if(result.length == 0){
                console.log('해당 아이디가 존재하지 않습니다.')
                let faLogin = req.session.loginFalse = true
                res.render('join',{loginFalse : faLogin})
            }
            else{
                if(result[0].USER_ID == id && result[0].USER_PW == pw){
                    console.log(result[0].USER_NICK,'님이 접속하였습니다.')

                    // 접속자 세션생성
                    let userName = result[0].USER_NAME
                    let userLevel = result[0].USER_LEVEL
                    let seName = req.session.userName = userName
                    let seLevel = req.session.userlevel = userLevel
                    let seLogin = req.session.login = true
                    res.render('main',{login : seLogin, name : seName, level : seLevel})

                }
                else{
                    console.log('로그인이 실패하였습니다.')
                    let faLogin = req.session.loginFalse = true
                    res.render('join',{loginFalse : faLogin})
                }
            }
        }
    })
})

<script>
    let loginFalse = '{{loginFalse}}'
    if(loginFalse){
        alert('아이디 또는 비밀번호를 확인해주세요')
    }
</script>