MySQL查询 - 编辑额外的字段

Question

我有3代表的产品，products_extra_fields，products_to_products_extra_fields

产品表

+-------------+--------------+---------------+ 
| products_id | categories_id| products_name | 
+-------------+--------------+---------------+ 
| 1   | 1   | product 1  | 
| 2   | 1   | product 2  | 
+-------------+--------------+---------------+ 

products_extra_fields表

+--------------------------+---------------------------+ 
| products_extra_fields_id | products_extra_fields_name| 
+--------------------------+---------------------------+ 
| 1      | sugar      | 
| 2      | cocoa      | 
| 3      | butter     | 
| 4      | milk      | 
+--------------------------+---------------------------+ 

products_to_products_extra_fields表

+-------------+---------------------------+-----------------------------+ 
| products_id | products_extra_fields_id | products_extra_fields_value | 
+-------------+---------------------------+-----------------------------+ 
| 1   | 1       | 20%       | 
| 1   | 2       | 45%       | 
| 1   | 3       | 27%       | 
| 2   | 1       | 12%       | 
+-------------+---------------------------+-----------------------------+ 

我想编辑产品1我使用此查询：

SELECT 
products_name, 
products_extra_fields_name, 
products_extra_fields_value FROM products, products_extra_fields, products_to_products_extra_fields 
WHERE products_to_products_extra_fields.products_extra_fields_id = products_extra_fields.products_extra_fields_id AND 
products_to_products_extra_fields.products_id=1 
GROUP BY products_extra_fields.products_extra_fields_id; 

+---------------+---------------------------+----------------------------+ 
| products_name | products_extra_fields_name| products_extra_fields_value| 
+---------------+---------------------------+----------------------------+ 
| product 1  | sugar      | 20%      | 
| product 1  | cocoa      | 45%      | 
| product 1  | butter     | 27%      | 
+---------------+---------------------------+----------------------------+ 

但我想看看

products_extra_fields_name（牛奶）没有价值

+---------------+---------------------------+----------------------------+ 
| products_name | products_extra_fields_name| products_extra_fields_value| 
+---------------+---------------------------+----------------------------+ 
| product 1  | sugar      | 20%      | 
| product 1  | cocoa      | 45%      | 
| product 1  | butter     | 27%      | 
| product 1  | milk      |       | 
+---------------+---------------------------+----------------------------+ 

和产品2可可，奶油，没有价值的牛奶只有糖12％

我能做些什么来得到结果我w蚂蚁。

看我的PHP脚本（products_edit2.php？ID = 1或2）

<?php 
require ('mysql/mysql_connect.php'); // Connect to the database. 
     if (is_numeric ($_GET['id'])) { 
    $query = "SELECT 
products_name, products_extra_fields_name, products_extra_fields_value FROM 
products, products_extra_fields, products_to_products_extra_fields WHERE 
products_to_products_extra_fields.products_extra_fields_id = products_extra_fields.products_extra_fields_id AND 
products_to_products_extra_fields.products_id = {$_GET['id']} 
GROUP BY products_extra_fields.products_extra_fields_id"; 

if ($result = mysql_query ($query)) { 

$query2 = "SELECT products_name FROM products WHERE products_id={$_GET['id']}"; 
if ($result2 = mysql_query ($query2)) { 
$row2 = mysql_fetch_array ($result2); 
$products_name = $row2['products_name']; 
?> 

<form action='products_edit.php' enctype='multipart/form-data' method='POST'> 
<table width="50%" border="0" cellpadding="2" cellspacing="2"> 
<tr> 
<td width="20%" align="right">PRODUCTS NAME:</td> 
<td><input type="text" name="products_name" size="80" value="<?php echo $products_name; ?>" /></td> 
</tr> 
<?php 
} 
/***** ***** *****/ 

while ($row = mysql_fetch_assoc ($result)) { 
$products_extra_fields_name = $row['products_extra_fields_name']; 
$products_extra_fields_value = $row['products_extra_fields_value']; 
$products_extra_fields_id = $row['products_extra_fields_id']; 
?> 
<tr> 
<td width="20%" align="right"><?php echo $products_extra_fields_id .'-'. $products_extra_fields_name; ?></td> 
<td><input type="text" name="categories_name" size="80" value="<?php echo $products_extra_fields_value; ?>" /></td> 
</tr> 

<?php } 

/***** ***** END *****/ 
?> 
<input type="hidden" name="categories_id" size="10" value="<?php echo $_GET['id']; ?>" /> 

<tr> 
<td width="100%" colspan="2" align="right"><input type="submit" name="submit" value="SAVE"/></td> 
</tr> 
</table> 
</form> 

<?php 
} else { // Couldn't get the information. 
print "<p>Could retrieve the entry because: <b>" . mysql_error() . "</b><br/><br/>. The query was $query.</p>"; 
} 
}else{ // No ID set. 
print '<p><b>You must have made a mistake in using this page.</b></p>'; 
} 
?> 

</body> 
</html> 

我想看到所有4 products_extra_fields_name和4个输入框（产品1有3个值1空，产品2有1值3 null）

Answer 1

当您在FROM中使用逗号分隔列表时，MySQL使用Inner Join。为了得到你想要的，你需要使用左连接。

SELECT 
products_name, 
products_extra_fields_name, 
products_extra_fields_value 
FROM products, products_extra_fields 
LEFT JOIN products_to_products_extra_fields 
ON products_to_products_extra_fields.products_extra_fields_id = products_extra_fields.products_extra_fields_id 
AND products_to_products_extra_fields.products_id=1 
GROUP BY products_extra_fields.products_extra_fields_id; 

这将产生：

+---------------+---------------------------+----------------------------+ 
| products_name | products_extra_fields_name| products_extra_fields_value| 
+---------------+---------------------------+----------------------------+ 
| product 1  | sugar      | 20%      | 
| product 1  | cocoa      | 45%      | 
| product 1  | butter     | 27%      | 
| product 1  | milk      | NULL      | 
+---------------+---------------------------+----------------------------+