Question

我有三张桌子（product，product_description，product_store_description）。

产品

此表有一行

+----------+---------------------+
|product_id|      description    |
+----------+---------------------+
|    1     |'regular description'|
+----------+---------------------+

PRODUCT_DESCRIPTION

此表有零行

+----------+-----------+--------+
|product_id|description|language|
+----------+-----------+--------+

product_store_description

This table has zero rows

+----------+-----------+--------+--------+
|product_id|description|language|store_id|
+----------+-----------+--------+--------+

我想为所有表.description返回WHERE product.product_id = '1'列。

所以在这种情况下我想要的输出是

$row = $result->fetch_assoc();
echo '<pre>';
var_dump($row);
echo '</pre>';

array (size=3)
    'p_description' => string 'regular description' (length=19)
    'pd_description' => string '' (length=0)
    'psd_description' => string '' (length=0)

我已经尝试了很多SQL的变体，这就是目前的情况。

SELECT p.description AS p_description ,pd.description AS pd_description, psd.description AS psd_description FROM product AS p 
RIGHT JOIN product_description AS pd ON(pd.product_id = p.product_id)
RIGHT JOIN product_store_description AS psd ON(psd.product_id = p.product_id) 
WHERE p.product_id = '1'
AND pd.language = 'en'
AND psd.language = 'en' AND psd.store_id = 1;

返回零行

我搜索了一个让我使用RIGHT JOIN的答案，但这并没有解决我的问题。

我已经创建了一个示例表的SQL小提琴HERE，不幸的是我还没有能够让任何人回答工作。

Answer 1

如果表product包含至少一个数据。并且您希望显示其他列NULL或自定义字符串，如"---"，您必须在查询中指定即使连接属性为空也要加入。因此，以下查询将为您提供数据。

SELECT
p.description AS p_description ,ifnull(pd.description,"---") AS pd_description,
ifnull(psd.description,"--") AS psd_description
FROM product AS p
LEFT JOIN Product_description AS pd ON(pd.product_id = p.product_id)
LEFT JOIN product_store_description AS psd ON(psd.product_id = p.product_id)
WHERE p.product_id = '1' AND (pd.language = 'en' or pd.language is null)
AND (psd.language = 'en' or psd.language is null) AND 
(psd.store_id = 1 or psd.store_id is null);

Answer 2

如果我理解正确，那么您需要LEFT join，因为产品表位于查询中联接的左侧。

左连接将返回连接运算符左侧表中的所有行，而右连接将返回连接运算符右侧表中的所有行。

Answer 3

如果您想接收一些数据，您应该执行以下查询：

SELECT 
   p.description AS p_description ,
   pd.description AS pd_description, 
   psd.description AS psd_description,
   pd.language as language,
   psd.store_id as store_id
FROM 
   product AS p LEFT JOIN product_description AS pd ON(pd.product_id = p.product_id) 
   LEFT JOIN product_store_description AS psd ON(psd.product_id = p.product_id) 
WHERE 
   p.product_id = '1'

但在这种情况下，您必须手动控制language和store_id的值

Mysql如果连接数据为空，如何返回行

3 个答案: