多个if语句工作，除非值为null。

Question

没有做很多php/mysql，但这看起来应该是一个简单的修复，我可能只是搞砸了一些小东西。很抱歉这么长时间的解释想要彻底

我有一个mysql数据库，里面满是健身测试结果，网站上有一个页面，显示登录人员的结果。

我们的设备收集的具体数据称为平衡对称，其结果要么是正数，要么是负数。如果一个人有-15%对称或更少，他们需要额外的工作在他们的左腿，如果他们是+15%对称或更少，他们需要更多的工作，他们的右腿。

这是一个非常重要的因素，所以我试图让他们知道在页面顶部的“红旗”。数据以负数或正数的形式存储在数据库中。

我基本上希望代码可以这样做：

- if the data is >= 15 then it spits out that they need more work on their right leg
- if the data is <= -15 then it spits out that they need more work on their left leg
- if the data is anything else, so between -14 and 14, or if it is null (sometimes they may not have done the balance part of the fitness test due to injury) then nothing is displayed

它与下面代码的工作方式是

- if >= 15 works perfectly tells them to work on their right leg
- if <= -15 works perfectly tells them to work on their left leg
- if between -14 and 14 works perfectly tells them nothing
- if null tells them to work on their left leg for some reason.  how do I make it so that the null value is handled the same way as the values between -14 and 14

<?php

if ($row['field_symmetry_value'] >= 15){
echo "              <div class='train_row1'>
           <div class='train_row_inside'>
            <div class='train_column1rf'><img src='http://racebattlerecover.com/images/redflag.png' /></div>
            <div class='train_column3rf'><h3>IMPORTANT: Your balance symmetry between your left and right leg is off by more than 15%. You need to add extra balance exercises to your right leg.</h3></div>
           </div>
          </div>";
}
elseif ($row['field_symmetry_value'] <= -15){
echo "              <div class='train_row1'>
           <div class='train_row_inside'>
            <div class='train_column1rf'><img src='http://racebattlerecover.com/images/redflag.png' /></div>
            <div class='train_column3rf'><h3>IMPORTANT: Your balance symmetry between your left and right leg is off by more than 15%. You need to add extra balance exercises to your left leg.</h3></div>
           </div>
          </div>";
}

?>

谢谢你的帮助！

Answer 1

我不知道为什么，但出于某种原因，null被认为不到-15。我认为null在数值比较中会被视为0，但显然不是。您可以很容易地修复这个问题：

else if (!is_null($row['field']) && $row['field'] <= -15) {

您还可以在查询中执行以下检查：

COALESCE(field_symmetry_value, 0)

如果field_symmetry_value是NULL，它将返回0，它不会打印任何内容。