我正在使用express在node.js中设置一个对象，并且我已经完成了创建和更新，但是我仍然停留在删除功能上

我试图从车把和/ delete的路由中分析代码，但仍然无法弄清为什么无法读取user_id

user_list_view.hbs：

<form id="add-row-form" action="/delete" method="post">
<div class="modal fade" id="DeleteModal" tabindex="-1" role="dialog" aria-labelledby="myModalLabel" aria-hidden="true">
    <div class="modal-dialog">
        <div class="modal-content">
            <div class="modal-header">
                <h5 class="modal-title" id="myModalLabel">Delete Product</h5>
                <button type="button" class="close" data-dismiss="modal" aria-label="Close"><span aria-hidden="true">&times;</span></button>
            </div>
            <div class="modal-body">
                <strong>Do you want to delete this data ?</strong>
            </div>
            <div class="modal-footer">
                <input type="hidden" name="user_id" class="form-control user_id" required>
                <button type="button" class="btn btn-default" data-dismiss="modal">Close</button>
                <button type="submit" class="btn btn-success">Delete</button>
            </div>
        </div>
    </div>
</div>

user_list_view.js中的jquery：

<script>
$(document).ready(function () {
    $('#mytable').on('click','.delete',function(){
        var user_id = $(this).data('user_id');
        $('#DeleteModal').modal('show');
        $('.user_id').val(user_id);
    });
})

process.js：

router.post('/delete',(req,res) => {
let sql = "DELETE FROM users WHERE user_id="+req.body.user_id
let query = db.query(sql,(err,results) => {
    if (err) throw err
    res.redirect('/user_list')
 })
})


module.exports = router

我希望结果能够基于user_id删除所选用户，但我收到了错误消息：

code: 'ER_PARSE_ERROR',errno: 1064,sqlMessage: "You have an error in your SQL syntax; check the manual that 
corresponds to your MariaDB server version for the right syntax to use 
near ''at line 1",sqlState: '42000',index: 0,sql: 'DELETE FROM users WHERE user_id='
}
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! latihan3@0.0.0 start: `node ./bin/www`
npm ERR! Exit status 1