Make a CTE from result of others CTE - sql

Question

I have several joined CTE. Something like:
;With CT1 AS(SELECT ..)
, CT2 AS(select)
SELECT *.T1,*T2 FROM CT1 T1 INNER JOIN CT2 T2 WHERE (some Condition ) GROUP BY (F1,F2, etc)
Now I need to join the result of this query to another CTE. What’s the best way? Can I make a CTE with the result of this Query? Any help would be greatly appreciated.

Answer 1

You can keep creating new CTEs based on previously defined ones. They may joined or otherwise combined, subject to the rules for CTEs.
; with
ArabicRomanConversions as (
select *
from ( values
( 0, '', '', '', '' ), ( 1, 'I', 'X', 'C', 'M' ), ( 2, 'II', 'XX', 'CC', 'MM' ), ( 3, 'III', 'XXX', 'CCC', 'MMM' ), ( 4, 'IV', 'XL', 'CD', '?' ),
( 5, 'V', 'L', 'D', '?' ), ( 6, 'VI', 'LX', 'DC', '?' ), ( 7, 'VII', 'LXX', 'DCC', '?' ), ( 8, 'VIII', 'LXXX', 'DCCC', '?' ), ( 9, 'IX', 'XC', 'CM', '?' )
) as Placeholder ( Arabic, Ones, Tens, Hundreds, Thousands )
),
Numbers as (
select 1 as Number
union all
select Number + 1
from Numbers
where Number < 3999 ),
ArabicAndRoman as (
select Number as Arabic,
( select Thousands from ArabicRomanConversions where Arabic = Number / 1000 ) +
( select Hundreds from ArabicRomanConversions where Arabic = Number / 100 % 10 ) +
( select Tens from ArabicRomanConversions where Arabic = Number / 10 % 10 ) +
( select Ones from ArabicRomanConversions where Arabic = Number % 10 ) as Roman
from Numbers ),
Squares as (
select L.Arabic, L.Roman, R.Arabic as Square, R.Roman as RomanSquare
from ArabicAndRoman as L inner join
ArabicAndRoman as R on R.Arabic = L.Arabic * L.Arabic
where L.Arabic < 16 ),
Cubes as (
select S.Arabic, S.Roman, S.Square, S.RomanSquare, A.Arabic as Cube, A.Roman as RomanCube
from Squares as S inner join
ArabicAndRoman as A on A.Arabic = S.Square * S.Arabic )
select *
from Cubes
order by Arabic
option ( MaxRecursion 3998 )

Answer 2

This is a format I have used a few times where a temp table is used to buffer one complex CTE which is output and then used again from temp with a second CTE.
It is useful if you need 2 result sets or if the complete CTE as one massive statement causes speed issues (breaking it up can be a huge performance improvement in some cases)
-- I do this "DROP" because in some cases where query is executed over and
-- over sometimes the object is not cleared before next transaction.
BEGIN TRY DROP TABLE #T_A END TRY BEGIN CATCH END CATCH;
WITH A AS (
SELECT 'A' AS Name, 1 as Value
UNION ALL SELECT 'B', 2
)
SELECT *
INTO #T_A
FROM A;
SELECT *
FROM #T_A ; -- Generate First Output Table
WITH B AS (
SELECT 'A' AS Name, 234 as Other
UNION ALL SELECT 'B', 456
)
-- Generate second result set from Temp table.
SELECT B.*, A. Value
FROM B JOIN #T_A AS A ON A.Name=B.Name
This produces a 2 table result set. Which is also handy in .NET filling a DataSet.