Question

我需要为这样的表编写mysql查询：

id | product_id | version | status 
 1 | 1          | 1       | 0
 2 | 1          | 2       | 1
 3 | 1          | 3       | 0
 4 | 2          | 9       | 0
 5 | 2          | 10      | 0

我需要获取行（对于product_id是唯一的 - 每个product_id一个）但是：
- 如果product_id有一行，状态= 1 - 抓住它 - 没有描述的行获取具有更高值或版本

的行

所以对于描述的表结果应该是

id | product_id | version | status 
 2 | 1          | 2       | 1
 5 | 2          | 10      | 0

我唯一的想法是获取状态为1的行，然后使用WHERE product_id NOT IN进行第二次查询，然后按版本DESC和GROUP BY product_id进行排序

Answer 1

在这种情况下可以加入表格

SELECT p1.id, p1.product_id, p1.version, p1.status FROM products p1
  LEFT OUTER JOIN (
    SELECT MAX(version) AS version FROM products p2
   ) p2 ON p1.version = p2.version OR p1.status = 1
GROUP BY p1.product_id

SQL Fiddle

Answer 2

您可以使用UNION

来实现

select myTable.id, product_id, version, status from myTable
where id in(select id from myTable where status > 0) 
union
select myTable.id, product_id, version, status from myTable
join (select max(id) as id from myTable group by product_id) 
as m on m.id = myTable.id 
and product_id  not in(select product_id from myTable where status > 0 )

MySQL获得第一个具有值的行或者获得另一个有序的行

2 个答案: