PHP 如果变量 = a 而不是 = b

Question

PHP 7.3.18MySQL 5.7.30这是相关的代码，它立即失败，所以我很感激它被纠正。第一个“如果”没问题，但问题出在第二个和第三个。$targetcatid2、$targetcatid3、$targetweight2、$targetweight3 已正确声明。目的是如果产品属于 Category2 而不是 Category3，则重量将变为 Weight2，反之亦然。$row2=mysqli_fetch_array($select2);if($row2['category_id']== $targetcatid){    $row['product_weight']= $targetweight;}if($row2['category_id']== $targetcatid2 && !== $targetcatid3){    $row['product_weight']= $targetweight2;}if($row2['category_id']== $targetcatid3 && !== $targetcatid2){    $row['product_weight']= $targetweight3;}我最近的努力是：如果($row2['category_id']== $targetcatid){ $row['product_weight']= $targetweight; }如果($row2['category_id']== $targetcatid2 && $row2['category_id']!== $targetcatid3){ $row['product_weight']= $targetweight2; }elseif($row2['category_id']== $targetcatid3 && $row2['category_id']!== $targetcatid2){ $row['product_weight']= $targetweight3; }elseif($row2['category_id']== $targetcatid2 && $row2['category_id']== $targetcatid3){ $row['product_weight']= $targetweight3; }我发现新条件不起作用，即使是单独使用也是如此。但是不明白为什么：elseif($row2['category_id'] == $targetcatid2 && $row2['category_id'] == $targetcatid3){ $row['product_weight'] = $targetweight3; }

Answer 1

您没有正确理解 && 运算符。

而不是这个

if($row2['category_id']== $targetcatid2 && !== $targetcatid3){

您应该分别比较条件。

if($row2['category_id']== $targetcatid2 && $row2['category_id'] !== $targetcatid3){