SqlServer 2005 T-SQL Query 学习笔记（3）

DECLARE @pagesize AS INT, @pagenum AS INT;
SET @pagesize = 5;
SET @pagenum = 2;

WITH SalesCTE AS
(
 SELECT ROW_NUMBER() OVER(ORDER BY qty, empid) AS rownum,
  empid, mgrid, qty
 FROM dbo.Sales
)
SELECT rownum, empid, mgrid, qty
FROM SalesCTE
WHERE rownum > @pagesize  (@pagenum-1)
 AND rownum <= @pagesize  @pagenum
ORDER BY rownum;

说明在上个例子中，其实SQL只审视了10行（25），也就是说，查看N页的话，SQL只查到N的页的数据，N页后面的数据一概不查看。

，每当移动一页，都会把这页放进缓存里，每次查询，就是逻辑查询（缓存）+物理查询的过程。物理查询只需要查询新请求的页即可，其他全部在缓存里执行，这样大大加快了查询速度。

MULTIPAGE ACCESS

如果结果集不是很大，而且分了多个请求页面，请求也不向前移动，那么这是一个好的方案在一个表里使用ROW_NUMBER具体化所有的页，然后创建一个群集索引。狼蚁网站SEO优化是例子。

SELECT ROW_NUMBER() OVER(ORDER BY qty, empid) AS rownum, empid, mgrid, qty INTO #SalesRN FROM dbo.Sales;

CREATE UNIQUE CLUSTERED INDEX idx_rn ON #SalesRN(rownum);

DECLARE @pagesize AS INT, @pagenum AS INT; SET @pagesize = 5; SET @pagenum = 2; 
SELECT rownum, empid, mgrid, qty FROM #SalesRN WHERE rownum BETWEEN @pagesize  
(@pagenum-1) + 1 AND @pagesize  @pagenum ORDER BY rownum;

SELECT empid, qty, RANK() OVER(ORDER BY qty) AS rnk, DENSE_RANK() OVER(ORDER BY qty) AS drnk FROM dbo.Sales ORDER BY qty;

SELECT empid, qty,
 CASE NTILE(3) OVER(ORDER BY qty, empid)
  WHEN 1 THEN 'low'
  WHEN 2 THEN 'medium'
  WHEN 3 THEN 'high'
 END AS lvl
FROM dbo.Sales
ORDER BY qty, empid;