如何在php中优化mysql嵌套循环查询

Question

我有两个表，一个是类别，另一个是products.Catid对于这两个表都是很常见的。我需要使用两个while循环来显示表中的数据。它的工作正常，但花费更多的时间，并抛出错误，如果它处理更多的类别。

<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 

更好逐个定义列，方便获取数据到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 

如果你想显示所有产品甚至catid已在类别被删除，你可以使用此项（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 

这就是您如何获取数据：

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

试试这个查询。它将列出所有类别的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> 

所以你的输出就会

catid catname  catproducts 

1  stationary book,pen 
2  leather  wallets,bags