How to reference one CTE twice?

问题:

I have a very fat common table expression which includes row numbers so that I can return a paged result set. I also want to return the total number of records that match the query before I page the result set.

with recs as (select *, row_number() over (order by id) as rownum from ......)
select * from recs where rownum between @a and @b .... select count(*) from recs

Obviously my query above is patchy, but it's just for illustrating my point. I want a page of results AND the total number of matches. How do I do this without having to literally copy and paste the entire 20+ line CTE?

回答1:

You can use commas to create multiple CTEs that references the CTEs Above.

Just to illustrate what I mean:

with recs as (
select 
    *, 
    row_number() over (order by id) as rownum from ......
    ),
counts as (
    select count(*) as totalrows from recs
)
select recs.*,count.totalrows
from recs
cross apply counts 
where rownum between @a and @b .... 

This is not the a good solution.

The best solution I found to have the total count in a CTE without counting the records is described in this article.

DECLARE @startRow INT; SET @startrow = 50;
WITH cols
AS
(
    SELECT table_name, column_name, 
        ROW_NUMBER() OVER(ORDER BY table_name, column_name) AS seq, 
        ROW_NUMBER() OVER(ORDER BY table_name DESC, column_name desc) AS totrows
    FROM [INFORMATION_SCHEMA].columns
)
SELECT table_name, column_name, totrows + seq -1 as TotRows
FROM cols
WHERE seq BETWEEN @startRow AND @startRow + 49
ORDERBY seq

回答2:

Don't think you can. From MSDN

A common table expression (CTE) can be thought of as a temporary result set that is defined within the execution scope of a single SELECT, INSERT, UPDATE, DELETE, or CREATE VIEW statement.

Emphasis on "single SELECT, INSERT, UPDATE, DELETE, or CREATE VIEW statement."

This might be a situation where you want to use a Temporary Table.

CREATE TABLE #Recs
{
  .....
}
INSERT INTO #Recs
select *, row_number() over (order by id) as rownum from ......

If you don't know the structure of the table before hand you can use this form to create a temporary table:

select *, row_number() over (order by id) as rownum INTO #Recs from ......

You will be able to use the Temporary table in the manner you have described above.

回答3:

You could append a field that has the total rows in it, of course it will be on every row

select recs.*,totalrows = (select count(0) from recs) 
from recs

回答4:

This is the best:

;WITH recs AS
(SELECT a,b,c,
      row_number() over (
                         ORDER BY id) AS RowNum,
                   row_number() over () AS RecordCount
FROM ......)
SELECT a,b,c,rownum,RecordCount FROM recs
WHERE rownum BETWEEN @a AND @b

回答5:

This is how we deal with paging (without session management for now) in a production environment. Performs as expected.

DECLARE
   @p_PageNumberRequested  int = 1,
      -- Provide -1 to retreive all pages with all the rows.
   @p_RowsPerPage          int = 25

;WITH Numbered AS (
SELECT
   ROW_NUMBER() OVER (ORDER BY YourOrdering) AbsoluteRowNumber
,  COUNT(1) OVER () TotalRows
,  YourColumns
FROM
   YourTable
),
Paged AS (
SELECT
   (AbsoluteRowNumber - 1) / @p_RowsPerPage + 1 PageNumber,
   *
FROM
   Numbered)
SELECT
   ROW_NUMBER() OVER(PARTITION BY PageNumber ORDER BY AbsoluteRowNumber) RowNumberOnPage,
   *
FROM
   Paged
WHERE
      PageNumber = @p_PageNumberRequested
   OR
      @p_PageNumberRequested = -1
ORDER BY 
   AbsoluteRowNumber