4

我正在写一个查询

SELECT * FROM EMPLOYEES WHERE EMP_ID IN (10,5,3,9,2,8,6)

我希望结果应按以下顺序

Emp_id   Emp_Name
10       John
5        Joe
3        Tippu
9        Rich
2        Chad
8        Chris
6        Rose

基本上与 IN 子句的顺序相同。有可能这样做吗？请告诉我。

PS：我可以在 SQL 中执行此操作，也可以在获得结果集后执行此操作，如果我可以使用 LINQ 或在前端进行排序的选项也对我有用（我在前端的数组中有 Emp ID）

谢谢

4

2 回答 2

4

字符串注释答案；这将给出与原始答案相同的结果，但匹配字符串：

  string orgList = "John,Joe,Tippu,Rich,Chad,Chris,Rose";
  List<string> orderArray = new List<string>(orgList.Split(",".ToCharArray()));

  // the linq to do the ordering
  var result = ourList.OrderBy(e => {
     int loc = orderArray.IndexOf(e.Name);
     return loc == -1? int.MaxValue: loc;
  });

作为旁注，这两行的原始答案可能会更好：

  string orgList = "10,5,3,9,2,8,6";
  List<int> orderArray = new List<int>(orgList.Split(",".ToCharArray()));

而不是使用整数常量。使用上面的代码将按任意逗号分隔的整数列表排序。

Linq 中的以下解决方案给出了以下结果：

在此处输入图像描述

void Main()
{
  // some test data
  List<Person> ourList = new List<Person>() 
  {
    new Person() { ID = 1, Name = "Arron" },
    new Person() { ID = 2, Name = "Chad" },
    new Person() { ID = 3, Name = "Tippu" },
    new Person() { ID = 4, Name = "Hogan" },
    new Person() { ID = 5, Name = "Joe" },
    new Person() { ID = 6, Name = "Rose" },
    new Person() { ID = 7, Name = "Bernard" },
    new Person() { ID = 8, Name = "Chris" },
    new Person() { ID = 9, Name = "Rich" },
    new Person() { ID = 10, Name = "John" }
  };

  // what we will use to order
  List<int> orderArray = new List<int>(){10,5,3,9,2,8,6};

  // the linq to do the ordering
  var result = ourList.OrderBy(e => {
     int loc = orderArray.IndexOf(e.ID);
     return loc == -1? int.MaxValue: loc;
  });

  // good way to test using linqpad (get it at linqpad.com
  result.Dump();
}

// test class so we have some thing to order
public class Person
{
   public int ID { get; set; }
   public string Name { get; set; }
}

原始的错误 SQL 答案

WITH makeMyOrder
(
   SELECT 10 as ID, 1 as Ord
     UNION ALL
   SELECT 5 as ID, 2 as Ord
     UNION ALL
   SELECT 3 as ID, 3 as Ord
     UNION ALL
   SELECT 9 as ID, 4 as Ord
     UNION ALL
   SELECT 2 as ID, 5 as Ord
     UNION ALL
   SELECT 8 as ID, 6 as Ord
     UNION ALL
   SELECT 6 as ID, 7 as Ord
),
SELECT * 
FROM EMPLOYEES E
JOIN makeMyOrder O ON E.EMP_ID = O.ID
ORDER BY O.Ord
于 2013-10-23T02:47:26.327 回答
2

什么，Linq-To-SQL 没有可以按下的神奇按钮来执行此操作？:-)

要在 SQL Server 中执行此操作，您需要一个将列表转换为集合并保持顺序的函数。给这只猫剥皮的方法有很多；这是一个：

CREATE FUNCTION dbo.SplitInts_Ordered
(
    @List       VARCHAR(MAX),
    @Delimiter  VARCHAR(255)
)
RETURNS TABLE
AS
    RETURN (SELECT [Index] = ROW_NUMBER() OVER (ORDER BY Number), Item 
    FROM (SELECT Number, Item = CONVERT(INT, SUBSTRING(@List, Number, 
        CHARINDEX(@Delimiter, @List + @Delimiter, Number) - Number))
      FROM (SELECT ROW_NUMBER() OVER (ORDER BY [object_id])
        FROM sys.all_objects) AS n(Number)
    WHERE Number <= CONVERT(INT, LEN(@List))
      AND SUBSTRING(@Delimiter + @List, Number, LEN(@Delimiter)) = @Delimiter
    ) AS y);
GO

现在你可以说：

DECLARE @list VARCHAR(MAX);

SET @list = '10,5,3,9,2,8,6';

SELECT e.Emp_Id, e.Emp_Name -- never use * in production code
  FROM dbo.Employees AS e -- always use schema prefix
  INNER JOIN dbo.SplitInts_Ordered(@list, ',') AS x
  ON x.Item = e.Emp_Id
  ORDER BY x.[Index];

更好的方法是完全停止传递逗号分隔的列表，并使用表值参数。这是一组东西，而不是字符串或一些 JSON 淫秽。在您的 C# 代码中创建一个 DataTable，其中包含两列，即列表和顺序。然后创建一个表类型：

CREATE TYPE dbo.SortedList AS TABLE(ID INT, [Order] INT);

然后是一个将其作为参数的存储过程：

CREATE PROCEDURE dbo.GetTheList
  @x dbo.SortedList READONLY
AS
BEGIN
  SET NOCOUNT ON;

  SELECT e.Emp_Id, e.Emp_Name
    FROM dbo.Employees AS e
    INNER JOIN @x AS x
    ON x.ID = e.Emp_Id
    ORDER BY x.[Order];
END
GO

您是否可以使用 Linq-To-SQL 做到这一点，我不确定；人们似乎很快就加入了 Linq 的潮流，因为它让事情变得如此简单。好吧，只要你不需要实际做任何事情。

于 2013-10-23T02:47:01.833 回答