CTE - LEFT OUTER JOIN Performance Problem - sql-server

Question

Using SQL Server 2017.
SQL FIDDLE: LINK
CREATE TABLE [TABLE_1]
(
PLAN_NR decimal(28,6) NULL,
START_DATE datetime NULL,
);
CREATE TABLE [TABLE_2]
(
PLAN_NR decimal(28,6) NULL,
PERIOD_NR decimal(28,6) NULL,
);
INSERT INTO TABLE_1 (PLAN_NR, START_DATE)
VALUES (1, '2020-05-01'), (2, '2020-08-05');
INSERT INTO TABLE_2 (PLAN_NR, PERIOD_NR)
VALUES (1, 1), (1, 2), (1, 5), (1, 6), (1, 5), (1, 6), (1, 17),
(2, 2), (2, 3), (2, 5), (2, 2), (2, 17), (2, 28);
CREATE VIEW ALL_PERIODS
AS
WITH rec_cte AS
(
SELECT
PLAN_NR, START_DATE,
1 period_nr, DATEADD(day, 7, START_DATE) next_date
FROM
TABLE_1
UNION ALL
SELECT
PLAN_NR, next_date,
period_nr + 1, DATEADD(day, 7, next_date)
FROM
rec_cte
WHERE
period_nr < 100
),
cte1 AS
(
SELECT
PLAN_NR, period_nr, START_DATE
FROM
rec_cte
UNION ALL
SELECT
PLAN_NR, period_nr, DATEADD(DAY, 1, EOMONTH(next_date, -1))
FROM
rec_cte
WHERE
MONTH(START_DATE) <> MONTH(next_date)
),
cte2 AS (
SELECT *, ROW_NUMBER() OVER (PARTITION BY PLAN_NR ORDER BY START_DATE) rn
FROM cte1
)
SELECT PLAN_NR, rn PERIOD_NR, START_DATE
FROM cte2
WHERE rn <= 100
Table_1 lists plans (PLAN_NR) and their start date (START_DATE).
Table_2 lists plan numbers (PLAN_NR) and periods (1 - X). Per plan number periods can appear several times but can also be missing.
A period lasts seven days, unless the period includes a change of month. Then the period is divided into a part before the end of the month and a part after the end of the month.
The view ALL_PERIODS lists 100 periods per plan according to this system.
My problem is the performance of the following select which I would like to use in a view:
SELECT
t2.PLAN_NR
, t2.PERIOD_NR
, a_p.START_DATE
from TABLE_2 as t2
left outer join ALL_PERIODS a_p on t2.PERIOD_NR = a_p.PERIOD_NR and t2.PLAN_NR = a_p.PLAN_NR
From about 4000 entries in TABLE_2 the select becomes incredibly slow.
The join itself does not yet slow down the query. Only with the additional select a_p.START_DATE everything becomes incredibly slow.
I read the view into a temporary table and did the join over that and got no performance issues. (2 seconds for the 4000 entries).
So I assume that the CTE used in the view is the reason for the slow performance.
Unfortunately I can't use temporary tables in views and I would hate to write the data to a normal table.
Is there a way in SQL Server to improve the CTE lag?

Answer 1

Instead of a recusive CTE, generate ALL_PERIODS with a CROSS join between the Plan table and a "number table" either persisted, or as a non-recursive CTE.
EG
WITH N As
(
select top 100 row_number() over (order by (select null)) i
from (values (1),(2),(3),(4),(5),(6),(7),(8),(9),(10) ) v1(i),
(values (1),(2),(3),(4),(5),(6),(7),(8),(9),(10) ) v2(i)
),
plan_period AS
(
SELECT
PLAN_NR, START_DATE,
N.i period_nr, DATEADD(day, 7*N.i, START_DATE) next_date
FROM TABLE_1 CROSS JOIN N
),

Answer 2

if you are able to modify the view I would recommend to do this :
add a table containing numbers starting from 0 to whatever you think you will need in database, you can use below command :
create table numbers ( id int)
go
;with cte (
select 0 num
union all
select num + 1
where num < 2000 -- change this
)
insert into number
from num from cte
change the first cte in the view to this :
WITH rec_cte AS
(
SELECT
PLAN_NR
, DATEADD(DAY, 7* id, START_DATE) START_DATE
, id +1 period_nr
, DATEADD(DAY, 7*( id+1), START_DATE) next_date
FROM
TABLE_1 t
CROSS apply intenum i
WHERE i.id <100
),...
Also consider using temp table instead of cte it might be helpful