如何在php中优化嵌套循环的mysql查询

Question

我有两个表，一个是category，另一个是products.Catid对于两个表都很常见。我需要使用两个while循环来显示表中的数据。它的工作正常，但如果处理更多类别，则会花费更多时间并抛出错误。

   <table>
<tr>
<?php
$cat=mysql_query("select * from category");
while($catquery=mysql_fetch_assoc($cat))
{?>
<td><?php echo $catquery['catid'] ?></td>
<td><?php echo $catquery['catname']?></td>
<?php 
 $catid=$catquery['catid'];
 }?>
<?php
$product=mysql_query("select * from product where catid=$catid");
 while($productquery=mysql_fetch_assoc($product))
{ 
?>
<td><?php echo $productquery['productname'] ?></td>
</tr>
</table>

Answer 1

select * from category a left join product b
on a.catid = b.catid

更好地逐列定义列，轻松将数据导入PHP，如：

select a.catid as category_catid, 
       a.catname as category_name,
       b.productname as product_productname
from category a left join product b
on a.catid = b.catid

如果您想显示所有产品，即使catid已被删除，您也可以使用此功能（与FULL JOIN相同）：

select a.catid as category_catid, 
       a.catname as category_name,
       b.productname as product_productname
from category a left join product b
on a.catid = b.catid
union
select a.catid as category_catid, 
       a.catname as category_name,
       b.productname as product_productname
from category a right join product b
on a.catid = b.catid

这是您获取数据的方式：

while($catquery=mysql_fetch_assoc($cat))
{?>
<td><?php echo $catquery['category_catid'] ?></td>
<td><?php echo $catquery['category_name']?></td>
<td><?php echo $catquery['product_productname']?></td>
....

Answer 2

尝试此查询。它将列出所有类别详细信息及其各自的产品名称（catproducts - 在以下查询中）。

<table>

<?php
$cat=mysql_query("select *,(select group_concat(productname) as catproducts from product where product.catid= category.catid) as catproducts from category");
while($catquery=mysql_fetch_assoc($cat)) { ?>
  <tr>
  <td><?php echo $catquery['catid']; ?></td>
  <td><?php echo $catquery['catname'];?></td>
  <td><?php echo $catquery['catproducts']; ?></td>
  </tr>
<?php }//end while ?>

</table>

所以你的输出将是

catid  catname      catproducts

1      stationary   book,pen
2      leather      wallets,bags