PHP用户提交的数据是不是要进入数据库？

My user submitted data will not go into my database, I have a form in which they insert their information, and then it should just insert into the database. I can connect to my database fine and it picks up the information, it just doesn't insert it?

The form:

<div class="form">
    <form id="addsteps" action="add.php" method="post" autocomplete="off">
         <div class="field-wrap">
             <input type="date" required autocomplete="off" name="date" style="color: black; text-align: center;"/>
          </div>
          <div class="field-wrap">
              <input type="number" required autocomplete="off" name="steps" style="color: black;"/>
          </div>
          <button type="submit" class="button button-block" name="submit" />Submit</button>
    </form>
</div>

The code:

<?php   include '../db_connection.php';

session_start();

$unique_id = $_SESSION['unique_id'];

$_SESSION['date'] = $_POST['date'];
$_SESSION['steps'] = $_POST['steps'];

$_POST['date'];
$_POST['steps'];

$date = $link->escape_string($_POST['date']);
$steps = $link->escape_string($_POST['steps']);

$sql = "INSERT INTO step_count (unique_id, date, steps) "
  . "VALUES ('$unique_id','$date','$steps')";

 ?>

It picks up the data fine and when using a var_dump I get

string(81) "INSERT INTO step_count (unique_id, date, steps) VALUES ('1','2017-12-16','12345')"

So I was just wondering where I am going wrong as it won't go into the database?

This is the db_connection file:

<?php
$link = mysqli_connect("localhost", "root", "", "repsandsteps");

 if (!$link) {
  echo "Error: Unable to connect to MySQL." . PHP_EOL;
  echo "Debugging errno: " . mysqli_connect_errno() . PHP_EOL;
  echo "Debugging error: " . mysqli_connect_error() . PHP_EOL;
  exit;
  } ?>

you should execute the query like this .

<?php   include '../db_connection.php';
session_start();

$unique_id = $_SESSION['unique_id'];
$_SESSION['date'] = $_POST['date'];
$_SESSION['steps'] = $_POST['steps'];

$date = mysqli_real_escape_string($link, $_POST['date']);
$steps = mysqli_real_escape_string($link, $_POST['steps']);

$sql = "INSERT INTO step_count (unique_id, date, steps) "
  . "VALUES ('$unique_id','$date','$steps')"; 

mysqli_query($link,$sql);