Mysql 从多个重复项中仅选择一条记录

Hello im使用下面的查询从数据库中选择一些元素

SELECT *,c.slug AS pslug,d.slug AS catslug 
FROM uhhu_virtuemart_products as a 
LEFT JOIN uhhu_virtuemart_products_el_gr as d 
    on a.virtuemart_product_id=d.virtuemart_product_id 
LEFT JOIN uhhu_virtuemart_product_categories as b 
    ON a.virtuemart_product_id = b.virtuemart_product_id 
LEFT JOIN uhhu_virtuemart_categories_el_gr AS c 
    ON b.virtuemart_category_id=c.virtuemart_category_id 
WHERE a.virtuemart_product_id = 508

问题是一个产品可以有很多类别，所以这个查询返回我3行，而我需要始终取1行作为输出

virtuemart\u产品\u类别：

我想要的是，当它在这里检查类别时：

左键将UHU\u virtuemart\u产品\u类别合并为b
在a.virtuemart\u product\u id=b.virtuemart\u product\u id上

写一个限制1语句

我尝试使用如下嵌套选择：

SELECT *,c.slug AS pslug,d.slug AS catslug
FROM uhhu_virtuemart_products as a 
WHERE uhhu_virtuemart_product_id =
    (SELECT virtuemart_product_id 
    from virtuemart_product_categories 
    where virtuemart_product_id=508 LIMIT 1)
LEFT JOIN uhhu_virtuemart_categories_el_gr AS c 
ON a.virtuemart_category_id=c.virtuemart_category_id
LEFT JOIN uhhu_virtuemart_categories_el_gr as d 
on c.virtuemart_category_id=d.virtuemart_category_id

就像这样：

   SELECT *,c.slug AS pslug,d.slug AS catslug 
FROM uhhu_virtuemart_product_categories as a
LEFT JOIN uhhu_virtuemart_products_el_gr as d 
on a.virtuemart_product_id=d.virtuemart_product_id 
LEFT JOIN uhhu_virtuemart_categories_el_gr AS c 
ON a.virtuemart_category_id=c.virtuemart_category_id 
WHERE a.virtuemart_product_id =( 
    SELECT virtuemart_product_id 
    from uhhu_virtuemart_product_categories as f 
    where f.virtuemart_product_id=508 
    LIMIT 1)

我也尝试过使用

SELECT distinct

，但它也不起作用。我只知道SQL的基础知识，找不到类似的方法来帮助我解决这个问题，所以我非常感谢您的帮助

---

希望我说得够清楚。

DISTINCT对所选的所有行都有效。右连接对大多数人来说太混乱了，所以我的建议是执行“主表左连接附加数据”。你想让我将右连接更改为左连接吗？你想用右连接实现什么？它连接新表（

d

）的所有行，即使是表

a

中没有相应键的行。这就是你想要的吗？似乎我读错了，那么正确的连接是什么：S我要编辑它你也可以按virtuemart\u product\u id分组