Mysql SQL：选择重复值的第一行

从以下代码：

SELECT
farm_products.id as ID,  
farm_products.product as Product1,  
shop_products.product as Product2
FROM  
farm_products,  
shop_products,  
shop_farm
WHERE
farm_products.id = shop_farm.farm_id and
shop_farm.farm_id = shop_products.id and 
farm_products.product != shop_products.product;

我得到以下输出：

+-------+----------+---------+
|ID     | Product1 | Product2|
+-------+----------+---------+
|06     | 'Apple'  | 'Grape' |
+-------+----------+---------+
|06     | 'Orange' | 'Grape' |
+-------+----------+---------+
|06     | 'Pear'   | 'Apple' |
+-------+----------+---------+
|07     | 'Apple'  | 'Pear'  |
+-------+----------+---------+
|08     | 'Kiwi'   | 'Grape' |
+-------+----------+---------+
|08     | 'Grape'  | 'Orange |
+-------+----------+---------+

我想要一张表，每个表中只出现第一行 ID出现

换句话说，我想要一个如下所示的输出：

+-------+----------+---------+
|ID     | Product1 | Product2|
+-------+----------+---------+
|06     | 'Apple'  | 'Grape' |
+-------+----------+---------+
|07     | 'Apple'  | 'Pear'  |
+-------+----------+---------+
|08     | 'Kiwi'   | 'Grape' |
+-------+----------+---------+

我曾尝试使用DISTINCT删除所有重复的ID，但这显然不起作用。 我希望尽量避免嵌套查询，并使代码尽可能简单

有人能帮忙吗？

使用排号

您可以按照下面的方式使用您的查询

 with cte as
(
SELECT
farm_products.id as ID,  
farm_products.product as Product1,  
shop_products.product as Product2,
row_number() over(partition by farm_products.id order by 
 farm_products.product) rn 
FROM  
farm_products join 
shop_products on farm_products.product != shop_products.product
join shop_farm on shop_farm.farm_id = shop_products.id
and farm_products.id = shop_farm.farm_id   

) select * from cte where rn=1

这将有助于：

select * from (SELECT
farm_products.id as ID,  
farm_products.product as Product1,  
shop_products.product as Product2,
row_number() over(partition by farm_products.id order by 
farm_products.id) rank 
FROM  
farm_products,  
shop_products,  
shop_farm
WHERE
farm_products.id = shop_farm.farm_id and  
shop_farm.farm_id = shop_products.id and  
farm_products.product != shop_products.product)
where rank=1
;

---

今天的提示：切换到现代的显式连接语法。更容易编写而不出错，更容易阅读和维护，并且在需要时更容易转换为外部联接。mysql版本？@Zaynulabadinuthin我相信我使用的是mysql 8.0.13.0您编写的第一个表是什么？输入输出您在查询中提到的表代表哪些表？什么决定了第一行？无法保证数据按表顺序排列，那么该如何对这些数据进行排序？为什么id 06的第1行是apple而不是橙色？@nikhilsugandh mysql 8+版本支持窗口函数

select * from (SELECT
farm_products.id as ID,  
farm_products.product as Product1,  
shop_products.product as Product2,
row_number() over(partition by farm_products.id order by 
farm_products.id) rank 
FROM  
farm_products,  
shop_products,  
shop_farm
WHERE
farm_products.id = shop_farm.farm_id and  
shop_farm.farm_id = shop_products.id and  
farm_products.product != shop_products.product)
where rank=1
;