Question

所以我一直在努力：

SELECT DISTINCT l.* 
  FROM StreamView l
  JOIN Friendships f ON f.Sender = @UserName OR f.Recipient = @UserName 
 WHERE l.Sender <> @UserName 
   AND l.Recipient <> @UserName 
   AND (   l.Sender = f.Recipient 
        OR l.Sender = f.Sender 
        OR l.Recipient = f.Sender 
        OR l.Recipient = f.Recipient) 
ORDER BY DateTime DESC

它非常适合获取所需记录的列表。无论如何，我希望能够为这个查询提供两个新属性，从哪个行开始获取记录，以及第二个定义长度的整数。

原因是我正在申请“懒惰滚动”。对这些数据的影响。

我想将这两个值添加到查询中：（Int32 startAt，Int32 howMany）

有什么想法吗？感谢。

Answer 1

这是一个几乎完整的解决方案：

DECLARE 
  @startat INT ,
  @howmany INT

SET @startat = 5
SET @howmany = 10;

WITH table1 AS
(
SELECT ROW_NUMBER() OVER(ORDER BY DateTime DESC) AS RowNumber, 
       l.* 
  FROM StreamView l
  JOIN Friendships f ON f.Sender = @UserName OR f.Recipient = @UserName 
 WHERE l.Sender <> @UserName 
   AND l.Recipient <> @UserName 
   AND (   l.Sender = f.Recipient 
        OR l.Sender = f.Sender 
        OR l.Recipient = f.Sender 
        OR l.Recipient = f.Recipient) 
)
SELECT * 
  FROM table1 
 WHERE RowNumber >= @startat 
   AND RowNumber < @startat + @howmany;

唯一缺少的是不同的方面，因为这会导致row_number出现问题。

你可以做的就是将select语句移动到一个函数中，该函数将执行不同的选择，然后在with语句中从中选择。

CREATE FUNCTION dbo.GetRecords(@UserName NVARCHAR(MAX)) RETURNS TABLE
AS
  RETURN (
    SELECT DISTINCT l.* 
      FROM StreamView l
      JOIN Friendships f ON f.Sender = @UserName OR f.Recipient = @UserName 
     WHERE l.Sender <> @UserName 
       AND l.Recipient <> @UserName 
       AND (   l.Sender = f.Recipient 
            OR l.Sender = f.Sender 
            OR l.Recipient = f.Sender 
            OR l.Recipient = f.Recipient) 

  )
GO

然后with语句中的select类似于：

SELECT ROW_NUMBER() OVER(ORDER BY DateTime DESC) AS RowNumber, 
       l.* 
  FROM dbo.GetRecords(@UserName)

对写入的SQL查询应用'LIMIT'之类的选项

1 个答案: