How to Reuse a Common Table Expression

How can I reuse a Common Table Expression

If you do not require them in 2 different queries, you can try

;with query as (
  Select Row_Number() over (Order By UserID ASC) as TableRowNum,
         FirstName,
         LastName
  From   Users
),
totalCount AS (
    SELECT COUNT(1) Total FROM query
)
Select  query.*,
        Total
from    query, totalCount 
where   TableRowNum 
between 1 and 25 
Order By TableRowNum ASC

If you do require 2 different queries, rather use a table var

DECLARE @User TABLE(
        TableRowNum INT,
        FirstName VARCHAR(50),
        LastName VARCHAR(50)
)
;with query as (
  Select Row_Number() over (Order By UserID ASC) as TableRowNum,
         FirstName,
         LastName
  From   Users
)
INSERT INTO @User
SELECT  TableRowNum,
        FirstName,
        LastName
FROM    query

SELECT  *
FROM    @User
where   TableRowNum 
between 1 and 25 
Order By TableRowNum ASC

SELECT COUNT(1) FROM @User

Reuse results from SQL Server common table expression

From the WITH common_table_expression manual:

Specifies a temporary named result set, known as a common table expression (CTE). This is derived from a simple query and defined within the execution scope of a single SELECT, INSERT, UPDATE, or DELETE statement.

So, no, you can't extend the scope of the CTE beyond the SELECT statement it was defined in. You will have to store the result in a temporary table or table valued variable if you want to use the result more than once.

Use one CTE many times

A CTE is basically a disposable view. It only persists for a single statement, and then automatically disappears.

Your options include:

• Redefine the CTE a second time. This is as simple as copy-paste from WITH... through the end of the definition to before your SET.

• Put your results into a #temp table or a @table variable

• Materialize the results into a real table and reference that

• Alter slightly to just SELECT COUNT from your CTE:

.

SELECT @total = COUNT(*)
FROM Players p 
INNER JOIN Teams t 
    ON p.IdTeam=t.Id 
INNER JOIN Leagues l 
    ON l.Id=t.IdLeague
WHERE l.Id=@idleague

How to reference one CTE twice?

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

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