如何在php中優化mysql嵌套循環查詢

Question

我有兩個表，一個是類別，另一個是products.Catid對於這兩個表都是很常見的。我需要使用兩個while循環來顯示錶中的數據。它的工作正常，但花費更多的時間，並拋出錯誤，如果它處理更多的類別。

<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 

更好逐個定義列，方便獲取數據到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 

如果你想顯示所有產品甚至catid已在類別被刪除，你可以使用此項（與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 

這就是您如何獲取數據：

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

試試這個查詢。它將列出所有類別的詳細信息及其各自的產品名稱（catproducts - 在以下查詢中）。

<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> 

所以你的輸出就會

catid catname  catproducts 

1  stationary book,pen 
2  leather  wallets,bags