Question

我想按升序选择最后两个元素，然后是第一个元素。这是我的代码

   SELECT products.*, locations.logo FROM 
    (SELECT products.* FROM 
    (SELECT products.* FROM products AS products  ORDER BY products.id DESC )
    AS products LEFT JOIN users ON users.id=products.userid WHERE users.hide=0)
    AS products LEFT JOIN locations ON products.location=locations.id LIMIT 2
    UNION SELECT products.*, locations.logo FROM 
    (SELECT products.* FROM 
    (SELECT products.* FROM products AS products  ORDER BY products.id ASC ) 
    AS products LEFT JOIN users ON users.id=products.userid WHERE users.hide=0)
    AS products LEFT JOIN locations ON products.location=locations.id LIMIT 3

E.g。我现在正在购买20种产品

20,19,1（按id排序）。

我想要19,20,1。

此时，上述声明根据例如。我知道我必须提出一个ORDER BY条款，但我不知道在我的审判中我的错误原因

"Incorrect usage of UNION and ORDER BY"

有人可以帮我吗？

Answer 1

你可以做这样的事情

SELECT id
  FROM
(
  (
    SELECT id, 0 sort_order
      FROM Table1
     ORDER BY id DESC
     LIMIT 2
  )
  UNION ALL
  (
    SELECT id, 1 sort_order
      FROM Table1
     ORDER BY id 
     LIMIT 1
  )
) q
 ORDER BY sort_order, id

输出：

| ID |
|----|
| 19 |
| 20 |
|  1 |

这是 SQLFiddle 演示

Mysql选择最后2个元素升序，然后是1st元素

1 个答案: