PHP 选择同时包含父项和子项

Question

当我查看包含父类别和子类别的下拉选择菜单时，它在 optgroup 标签内的所有父类别显示不正确，如下所示：

**Cat1 Cat2 Cat3** 
 - Sub
 - Sub 
 - Sub

我的意图是这样的：

**Cat**
 - Sub
**Cat**
 - Sub

等等……

任何想法我需要做什么才能正确显示。

这是当前代码：

<select name="DeleteSubCategory" class="form-control" data-style="btn-new">
	<optgroup label="
		<?php
		require('functions/connect.php');
         $stmt = $connect->prepare("SELECT CategoryID, CategoryName FROM category ORDER BY CategoryName ASC");
		$stmt->execute();
		$stmt->bind_result($CategoryID, $CategoryName);
		while ($stmt->fetch()){
		echo "$CategoryName";
		}
		$stmt->close();
		?>">
		
		<?php
		require('functions/connect.php');
		$stmt = $connect->prepare("SELECT SubCategoryID, SubCategoryParentID, SubCategoryName FROM subcategory");
		$stmt->execute();
		$stmt->bind_result($SubCategoryID, $SubCategoryParentID, $SubCategoryName);
		while ($stmt->fetch()){
		echo "<option value='$SubCategoryID'>$SubCategoryName</option>";
		}
		$stmt->close();
		?>
	</optgroup>					
</select>

在下面的反馈之后，我加入了我的查询，该查询按要求显示:)

<?php
		require('functions/connect.php');
		$stmt = $connect->prepare("SELECT 
		category.CategoryID,
		category.CategoryName,
		subcategory.SubCategoryID, 
		subcategory.SubCategoryParentID,
		subcategory.SubCategoryName
		FROM category
		INNER JOIN subcategory ON category.CategoryID = subcategory.SubCategoryParentID");
		$stmt->execute();
		$stmt->bind_result($CategoryID, $CategoryName, $SubCategoryID, $SubCategoryParentID, $SubCategoryName);
		?>
  <select name="DeleteSubCategory" class="form-control" data-style="btn-new">
	<?php
		while ($stmt->fetch()){
		?>
	
	<optgroup label="<?php echo $CategoryName; ?>">
       <option value= "<?php echo $SubCategoryID; ?>"><?php echo $SubCategoryName; ?></option>
	</optgroup>	
		<?php
		}
		$stmt->close();
		?>	
      </select>

Answer 1

嵌套循环可以解决问题，但它很混乱，而且维护起来很头疼。您不使用 Join 有什么原因吗？如果每个类别都可以有一个子类别，为什么不共享一个索引 ID 并使用连接呢？这将使格式化更加容易。

https://dev.mysql.com/doc/refman/5.7/en/join.html