通过连接表的SQL Order By

时间:2018-08-23 21:09:31

标签: mysql sql sql-order-by

我对相关产品有一个简单的设置。我的数据库有两个表:

product表和id, name列和联结表product_assignmentsproduct_id, related_id, order列。

我需要获取所有相关产品,并按order列进行排序

SELECT * FROM `products` LEFT JOIN
`related_assignments` `ra` ON `products`.`id` =
`ra`.`product_id` WHERE `id` IN (412, 1663, 1928) ORDER BY
`ra`.`order` DESC

我没有看到任何错误,我得到了所有三个记录(412、1663和1928年),但是是按其ID而不是按顺序字段排序的。

如何用一个SQL请求对它们进行排序?

产品

+------+-------+
|  id  | name  |
+------+-------+
|  412 | Watch |
| 1663 | Book  |
| 1928 | Phone |
| 2000 | Cup   |
+------+-------+

相关

+------------+------------+-------+
| product_id | related_id | order |
+------------+------------+-------+
|       2000 |        412 |     1 |
|       2000 |       1663 |     2 |
|       2000 |       1928 |     0 |
+------------+------------+-------+

1 个答案:

答案 0 :(得分:3)

根据示例数据和预期结果,您似乎需要使用ra.related_id作为连接条件,而不是ra.product_id

Left join上使用products.id =ra.product_id时,它仅返回id = 2000行数据。但是您的where子句使用id IN (412, 1663, 1928),这将使ra.order都为null,这样order by ra.order将一无所有。

create table products(
   id int,
   name varchar(50)
);



insert into products values ( 412, 'Watch');
insert into products values (1663, 'Book ');
insert into products values (1928, 'Phone');
insert into products values (2000, 'Cup  ');


create table Related(
   product_id int,
  related_id  int,
   `order` int
);

insert into Related values (2000,  412 ,1 );
insert into Related values (2000, 1663 ,2 );
insert into Related values (2000, 1928 ,0 );

查询1

SELECT * 
FROM `products` LEFT JOIN
`Related` `ra` ON `products`.`id` =
`ra`.`related_id` 
WHERE `id` IN (412, 1663, 1928) 
ORDER BY `ra`.`order` DESC

Results

|   id |  name | product_id | related_id | order |
|------|-------|------------|------------|-------|
| 1663 | Book  |       2000 |       1663 |     2 |
|  412 | Watch |       2000 |        412 |     1 |
| 1928 | Phone |       2000 |       1928 |     0 |