Create calendar function in Oracle using WITH STATEMENT - sql

Question

I come from SQL Server and some times I'm not familiar to Oracle syntax, I want to create a function that takes a date and number of dates as a parameters and create a table function.
My original query is:
VAR TREND = 1;
VAR OBS_DATE = 20221109;
VAR N_DAYS = 21;
WITH CAL AS
(
SELECT
TO_DATE(:OBS_DATE, 'YYYYMMDD') + (LEVEL - 1 * :TREND) DT, ROW_NUMBER() OVER(ORDER BY NULL) - 1 IX
FROM
DUAL
WHERE
TO_CHAR(TO_DATE(:OBS_DATE, 'YYYYMMDD') + (LEVEL - 1 * :TREND) , 'D') NOT IN (1,7)
CONNECT BY LEVEL <= :N_DAYS + :N_DAYS/5*2+1
)
SELECT DT
FROM CAL
WHERE IX <= :N_DAYS;
But when I try to convert as a function it sends me an error and I don't know what the correct syntax is.
My attempt is:
CREATE OR REPLACE FUNCTION FUN_BUS_CALENDAR(
OBS_DATE IN DATE := SYSDATE
, NDAYS IN NUMBER
, TREND IN NUMBER
)
RETURN OBS_DATE DATE;
BEGIN
WITH CAL AS(
SELECT
TO_DATE(:OBS_DATE, 'YYYYMMDD') + (LEVEL - 1 * :TREND) OBS_DATE, ROW_NUMBER() OVER(ORDER BY NULL) - 1 IX
FROM DUAL
WHERE TO_CHAR(TO_DATE(:OBS_DATE, 'YYYYMMDD') + (LEVEL - 1 * :TREND) , 'D') NOT IN (1,7)
CONNECT BY LEVEL <= :N_DAYS + :N_DAYS/5.*2.+1.
)
SELECT OBS_DATE FROM CAL WHERE IX <= :N_DAYS
RETURN OBS_DATE
END
/

Answer 1

You should probably just use the initial query.
However, if you did want a function then you can use a pipelined function:
CREATE FUNCTION BARRRAF.FUN_BUS_CALENDAR(
OBS_DATE IN DATE := SYSDATE,
NDAYS IN NUMBER,
TREND IN NUMBER
) RETURN SYS.ODCIDATELIST PIPELINED
IS
BEGIN
FOR i IN 1 .. ndays LOOP
PIPE ROW( obs_date + i - trend );
END LOOP;
END;
/
Then if you want to generate a row number then just use a sub-query:
SELECT column_value AS obs_date,
ROWNUM - 1 AS rn
FROM TABLE(BARRRAF.FUN_BUS_CALENDAR(ndays => 3, trend=>1))
Which outputs:
OBS_DATE
RN
2022-11-17 23:40:22
0
2022-11-18 23:40:22
1
2022-11-19 23:40:22
2
fiddle

Answer 2

Here is a generic function that can be used to create a calendar for the following INTERVALs seconds, minutes, hours or days.
You can pass it any start and END date/time you like. The lower or higher date can go in any position as there is logic to figure out which is what least/greatest command
CREATE OR REPLACE FUNCTION generate_dates(i_from_dat IN TIMESTAMP, i_to_dat IN TIMESTAMP, i_interval IN NUMBER, i_interval_type IN VARCHAR2)
RETURN VARCHAR2
SQL_MACRO
IS
BEGIN
RETURN q'~SELECT LEAST(i_from_dat,i_to_dat) + NUMTODSINTERVAL( (LEVEL-1)*i_interval, i_interval_type ) AS dt
FROM DUAL
CONNECT BY LEAST(i_from_dat,i_to_dat) + NUMTODSINTERVAL( (LEVEL-1)*i_interval, i_interval_type) < GREATEST(i_from_dat, i_to_dat)~';
END ;
SELECT * FROM generate_dates(
TIMESTAMP '2022-11-03 09:47:31',
TIMESTAMP '2022-11-03 12:37:11',
30, 'MINUTE') ;
DT
03-NOV-22 09.47.31.000000 AM
03-NOV-22 10.17.31.000000 AM
03-NOV-22 10.47.31.000000 AM
03-NOV-22 11.17.31.000000 AM
03-NOV-22 11.47.31.000000 AM
03-NOV-22 12.17.31.000000 PM
SELECT * FROM generate_dates(
TIMESTAMP '2022-11-03 00:00:00',
TIMESTAMP '2022-11-08 00:00:00',
1, 'DAY') ;
DT
03-NOV-22 12.00.00.000000 AM
04-NOV-22 12.00.00.000000 AM
05-NOV-22 12.00.00.000000 AM
06-NOV-22 12.00.00.000000 AM
07-NOV-22 12.00.00.000000 AM