AJAX POST数据到PHP MYSQli插入-插入表值为零

Question

我有一个jQuery＆AJAX脚本，该脚本正在抓取并将一些数据从HTML表传递到PHP脚本，然后将数据插入到我的表中...单击该按钮时，除检查数据库中的表是否为0。

startBalance1在HTML表中的值为1000。

HTML

<table class="forecast table table-striped" id="forecast" onload="myfunction()">
                        <tr><th scope="col">Month</th><th scope="col">Month Start</th><th scope="col">Investment</th><th scope="col">Return</th><th scope="col">Fee</th><th scope="col">Vat</th><th scope="col">Closing Balance</th><th scope="col">Month End</th></tr>

          <tr><td>1</td><td class="date-forecast"></td>

          <td><span>£</span><span id="startBalance1"></span></td>
          <td><span>£</span><span id="simpleInt1"></span></td>
          <td><span>£</span><span id="profitfee1"></span></td>
          <td><span>£</span><span id="afterVAT1"></span></td>
          <td><span>£</span><span id="amount1"></span></td>
          <td class="date-forecast">Wed Jul 10 2019</td></tr>

    <button type="button" name="submitfc" id="submitfc" class="btn btn-info mb-3" onclick="submitfc()">Save Forecast</button> 

AJAX

function submitfc() {     
   var startBalance1 = $("startBalance1").val();
    $.ajax({
        url:"test-new.php",
        type:"POST",
         data:{startBalance_1:startBalance1},
        success: function(data){
            alert('success');
        }
    });
};

PHP

$connection = mysqli_connect("****", "
****", "****", "****");
    if (!$connection) {
        die("Database connection failed: " . mysqli_connect_error());
    }

    $startBalance_1 = $_POST['startBalance_1'];

$query = "insert into clientCashout(startBalance) values ('$startBalance_1')";

$result = mysqli_query($connection, $query);