如何在单独的数据集中获取cte的rowcount？

Question

我已经确定了一种使用CTE和Row_Number函数从数据库中获取快速分页结果的方法,如下所示......

DECLARE @PageSize INT = 1
DECLARE @PageNumber INT = 2

DECLARE @Customer TABLE (
  ID       INT IDENTITY(1, 1),
  Name     VARCHAR(10),
  age      INT,
  employed BIT)

INSERT INTO @Customer
    (name,age,employed)
SELECT 'bob',21,1
    UNION ALL
SELECT 'fred',33,1
    UNION ALL
SELECT 'joe',29,1
    UNION ALL
SELECT 'sam',16,1
    UNION ALL
SELECT 'arthur',17,0;


WITH cteCustomers
     AS ( SELECT
            id,
            Row_Number( ) OVER(ORDER BY Age DESC) AS Row
          FROM   @Customer
          WHERE  employed = 1 
     /*Imagine I've joined to loads more tables with a really complex where clause*/
     )       

SELECT
  name,
  age,
  Total = ( SELECT
              Count( id )
            FROM   cteCustomers )
FROM       cteCustomers
INNER JOIN @Customer cust
  /*This is where I choose the columns I want to read, it returns really fast!*/
  ON cust.id = cteCustomers.id
WHERE      row BETWEEN ( @PageSize * @PageNumber - 1 ) AND ( @PageSize * ( @PageNumber ) )
ORDER      BY row ASC

使用这种技术,即使在复杂的连接和过滤器上,返回的结果也非常快.

要执行分页,我需要知道完整CTE返回的总行数.我通过放置一个包含它的列来"装箱"

Total = ( SELECT
              Count( id )
            FROM   cteCustomers )

有没有更好的方法来返回不同结果集中的总数而不将其归入列中？因为它是CTE,我似乎无法将其纳入第二个结果集.

Answer 1

如果不先使用临时表,我会使用CROSS JOIN来降低COUNT上逐行评估的风险

要获得总行数,需要单独对WHERE进行

WITH cteCustomers
     AS ( SELECT
            id,
            Row_Number( ) OVER(ORDER BY Age DESC) AS Row
          FROM   @Customer
          WHERE  employed = 1 
     /*Imagine I've joined to loads more tables with a really complex where clause*/
     )       

SELECT
  name,
  age,
  Total
FROM       cteCustomers
INNER JOIN @Customer cust
  /*This is where I choose the columns I want to read, it returns really fast!*/
  ON cust.id = cteCustomers.id

CROSS JOIN

(SELECT Count( *) AS Total FROM   cteCustomers ) foo

WHERE      row BETWEEN ( @PageSize * @PageNumber - 1 ) AND ( @PageSize * ( @PageNumber ) )
ORDER      BY row ASC

但是,这并不能保证给出准确的结果,如下所示:
我可以从sql server中的一个sql查询中获取count()和行吗？

编辑:经过几点评论.

如何避免CROSS JOIN

WITH cteCustomers
     AS ( SELECT
            id,
            Row_Number( ) OVER(ORDER BY Age DESC) AS Row,
            COUNT(*) OVER () AS Total --the magic for this edit
          FROM   @Customer
          WHERE  employed = 1 
     /*Imagine I've joined to loads more tables with a really complex where clause*/
     )       

SELECT
  name,
  age,
  Total
FROM       cteCustomers
INNER JOIN @Customer cust
  /*This is where I choose the columns I want to read, it returns really fast!*/
  ON cust.id = cteCustomers.id
WHERE      row BETWEEN ( @PageSize * @PageNumber - 1 ) AND ( @PageSize * ( @PageNumber ) )
ORDER      BY row ASC

注:YMMV的性能取决于2005或2008,Service Pack等

编辑2:

SQL Server Central显示另一种技术,您可以使用反向ROW_NUMBER.看起来很有用