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多个升序在Mysql中不起作用

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我有一个名为 request 的表，有三个列称为 Id, want, teach . 我必须按升序显示 want 和 teach 列，我不想显示NULL和空行 .

我尝试查询只有 want 列按升序显示，但 teach 列未按升序显示 .

SELECT want, teach FROM request WHERE want IS NOT NULL OR want !='' AND teach IS NOT NULL OR teach !='' GROUP BY want, teach ORDER BY want ASC, teach ASC

如果我写ORDER BY教ASC，想要ASC然后教学列以升序显示并想要显示DESC命令 . 你能帮帮我吗？

Chech左侧列是想要和右侧列教 . 我得到这样的输出 . 左侧列是ASC订单但右侧显示DESC
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mysql sorting

2 回答

  • 0

    首先，您需要了解订单

    如果你给第1个，第2个asc命令它会在第1列中排出并依赖于它将asc第2列 . 例如

    1st  2nd               
1    b
2    d
3    a
2    a
1    a

    通过转换来订购

    1st   2nd 
  1     a
  1     b
  2     a
  2     d
  3     a

    所以你需要不同的查询

    SELECT want FROM request WHERE want IS NOT NULL OR want !='' GROUP BY 
 want ORDER BY want ASC

     SELECT teach FROM request WHERE teach IS NOT NULL OR teach !='' GROUP
 BY  teach ORDER BY teach ASC
    回复于
  • 0

    你在这里没有得到多重订单的意义 .

    首先，默认情况下，大多数dbms排序为 ASC .

    多次排序取决于排序列的顺序，这意味着 - 或者说 - ： -

    " hey sql ! select some result from my table , order them by col1 and group them by this order , then this sorted or grouped data set , sort them by col2. "

    可以这么说，这是多维排序 .

    以此为例：

    +------+---------+-------+                   +------+---------+-------+
|  id  |   want  | teach |                   |  id  |   want  | teach |
+------+---------+-------+                   +------+---------+-------+
|   1  |    1    |   2   |    ORDER BY       |   2  |    1    |   1   |
|   2  |    1    |   1   |       want asc,   |   1  |    1    |   2   |
|   3  |    2    |   1   |       teach asc   |   4  |    1    |   2   |
|   4  |    1    |   2   |                   |   3  |    2    |   1   |
+------+---------+-------+                   +------+---------+-------+

    当你恢复排序列的顺序时，如下所示：

    +------+---------+-------+                   +------+---------+-------+
|  id  |   want  | teach |                   |  id  |   want  | teach |
+------+---------+-------+                   +------+---------+-------+
|   1  |    1    |   2   |    ORDER BY       |   2  |    1    |   1   |
|   2  |    1    |   1   |       teach asc,  |   3  |    2    |   1   |
|   3  |    2    |   1   |       want asc    |   1  |    1    |   2   |
|   4  |    1    |   2   |                   |   4  |    1    |   2   |
+------+---------+-------+                   +------+---------+-------+
    回复于

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