Question

我想交换列的值以对它们进行排序。

表：

if(CONDITION TO REMOVE) {
    print("deleting function...")
    df <- df[-c(df[,'Num2']),]
  }

结果应该是：

pid | category1 | category2 | category3
----+-----------+-----------+----------
 1  |    a      |    b      |
 2  |    b      |    a      |
 3  |    a      |    c      |    b

我的方法是选择行到列，按组排序并返回新列：

pid | category1 | category2 | category3
----+-----------+-----------+----------
 1  |    a      |    b      |
 2  |    a      |    b      |
 3  |    a      |    b      |    c

我找到了枢轴功能，但在这种情况下并没有真正理解如何使用它。

Answer 1

Sean Lange对于如何纠正数据库架构是正确的。

在此之前，您可以通过以下方式获取结果：

使用cross apply(values ...)将您的数据与row_number()一同取消，以便在common table expression内重新排序category;然后使用条件聚合重新编译该数据：

;with cte as (
select 
    t.pid
  , u.category
  , rn = row_number() over (partition by t.pid order by u.category)
from t
  cross apply (values (category1),(category2),(category3)) u(category)
where nullif(u.category,'') is not null  
)
select 
    pid
  , category1 = max(case when rn = 1 then category end) 
  , category2 = max(case when rn = 2 then category end) 
  , category3 = max(case when rn = 3 then category end)
from cte
group by pid

rextester演示：http://rextester.com/GIG22558

返回：

+-----+-----------+-----------+-----------+
| pid | category1 | category2 | category3 |
+-----+-----------+-----------+-----------+
|   1 | a         | b         | NULL      |
|   2 | a         | b         | NULL      |
|   3 | a         | b         | c         |
+-----+-----------+-----------+-----------+

Answer 2

您可以按以下方式进行转动

class Dog : Animal {
    private (set) var limbs: Int = 4
    private (set) var weight: Int = 50  // Error: Setter for property 'weight' must be declared internal because it matches a requirement in internal protocol 'Animal'
}

输出如下：

select * from (
    select *, RowN = row_number() over(partition by pid order by Category) from Categories
    ) a
    pivot (max(category) for RowN in ([1],[2],[3])) p

对于动态列列表，您可以使用如下：

+-----+-----------+-----------+-----------+
| Pid | Category1 | Category2 | Category3 |
+-----+-----------+-----------+-----------+
|   1 | a         | b         | NULL      |
|   2 | a         | b         | NULL      |
|   3 | a         | b         | c         |
+-----+-----------+-----------+-----------+

SQL Server：连续排序cols

2 个答案: