问当只需要一行值时，由AJAX、PHP和CSS创建的表会发送所有表单值

EN

<style>
            .table { display: table; } 
            .table>* { display: table-row; }
            .table>*>* { display: table-cell; padding: 5px; border-style: inset;}        
</style>
         <div class="table">
            <div>
               <div><b>Event Id</b></div>
               <div><b>Date</b></div>
               <div><b>@username</b></div>
               <div><b>Sign Up!</b></div>
            </div>
            <form id="form12" method="post">
               <div>12</div>
               <div>Feb-26-2021</div>
               <div><input class="formSignup" type="text" name="pi_username" id="pi_username" maxlength="20" placeholder="@username" form="form12"></div>
               <div><input class="formSignup" type="hidden" name="event_id" id="event_id" value="12" form="form12">
                  <input name="submit12" type="submit" value="Sign up!" onclick="signup(); return false;">
               </div>
            </form>
            <form id="form13" method="post">
               <div>13</div>
               <div>Feb-27-2021</div>
               <div><input class="formSignup" type="text" name="pi_username" id="pi_username" maxlength="20" placeholder="@username" form="form13"></div>
               <div><input class="formSignup" type="hidden" name="event_id" id="event_id" value="13" form="form13">
                  <input name="submit13" type="submit" value="Sign up!" onclick="signup(); return false;">
               </div>
            </form>
         </div>