Add subquery in query - Oracle SQL - sql

Question

My query return all days in month.
SELECT
EXTRACT( DAY FROM day ) ||' '|| substr(TO_CHAR( day, 'fmDAY' ),0,3) AS day,
EXTRACT( DAY FROM day ) as day_id
FROM (
WITH temp ( col ) AS (
SELECT to_date(2, 'mm') --2 is February
FROM dual
)
SELECT col + level - 1 AS day
FROM temp
CONNECT BY level <= last_day(col) - col + 1
ORDER BY day
)
How get all days from query where DAY_ID not in ==> (Select day_id from table1)
Eg. table1 return 5,10,15
Query resault need to display all days except 5,10,15

Answer 1

You can generate your calendar and then use NOT EXISTS:
WITH month ( col ) AS (
SELECT ADD_MONTHS(TRUNC(SYSDATE, 'YYYY'), 2 - 1)
FROM DUAL
),
calendar ( day, end_day ) AS (
SELECT col, LAST_DAY(col)
FROM month
UNION ALL
SELECT day + INTERVAL '1' DAY, end_day
FROM calendar
WHERE day < end_day
)
SELECT EXTRACT( DAY FROM day ) ||' '|| TO_CHAR( day, 'fmDY' ) AS day,
EXTRACT( DAY FROM day ) as day_id
FROM calendar c
WHERE NOT EXISTS (
SELECT 1
FROM table1 t
WHERE c.day = t.day_id
)
ORDER BY c.day;
Which, for your sample data:
CREATE TABLE table1 ( day_id ) AS
SELECT DATE '2021-02-05' FROM DUAL UNION ALL
SELECT DATE '2021-02-10' FROM DUAL UNION ALL
SELECT DATE '2021-02-15' FROM DUAL;
Outputs:
DAY
DAY_ID
1 MON
1
2 TUE
2
3 WED
3
4 THU
4
6 SAT
6
7 SUN
7
8 MON
8
9 TUE
9
11 THU
11
12 FRI
12
13 SAT
13
14 SUN
14
16 TUE
16
17 WED
17
18 THU
18
19 FRI
19
20 SAT
20
21 SUN
21
22 MON
22
23 TUE
23
24 WED
24
25 THU
25
26 FRI
26
27 SAT
27
28 SUN
28
db<>fiddle here

Answer 2

One way to generate all rows in month for dates in another table is to use a recursive CTE:
create table table1 as
select date '2021-04-16' as day_in from dual;
with cte (dte) as (
select trunc(day_in, 'MON') as dte
from table1
union all
select dte + interval '1' day
from cte
where dte < last_day(dte)
)
select *
from cte;
Here is a db<>fiddle.
EDIT:
If you want the days not in a table, then use:
with cte (dte) as (
select date '2021-02-01' as dte
from dual
union all
select dte + interval '1' day
from cte
where dte < last_day(dte)
)
select dte
from cte
where not exists (select 1 from table1 t1 where t1.day_id = cte.dte);
You can also use not exists using your query, but I find the recursive CTE easier to follow -- and it is standard SQL.