No hard coding in where clause in oracle - oracle

Question

[I have created a table as shown in figure
CREATE TABLE TABLE1 (CAL_YEAR VARCHAR2(4), NAME VARCHAR2(1))
INSERT INTO TABLE1 VALUES(‘2020’, ’A’)
INSERT INTO TABLE1 VALUES(‘2020’, ’B’)
INSERT INTO TABLE1 VALUES(‘2020’, ’C’)
INSERT INTO TABLE1 VALUES(‘2020’, ’D’)
INSERT INTO TABLE1 VALUES(‘2021’, ’E’)
INSERT INTO TABLE1 VALUES(‘2021’, ’F’)
Let us assume I am querying the statement in this year like
SELECT * FROM TABLE1 WHERE CAL_YEAR= TO_CHAR((SYSDATE),'YYYY');
so I get present year values.
What I need is if the present year data not present in the table then I need to use previous year data i.e. 2020 data...How can I do this in the where clause itself]1

Answer 1

You can simply get the maximum year that is less than or equal the year you query for in a subquery.
SELECT *
FROM table1
WHERE cal_year = (SELECT max(cal_year)
FROM table1
WHERE cal_year <= 2020);

Answer 2

You want to show the previous year, if no row for the current year exists? Simply select all years until now, order by year, take the last one.
SELECT *
FROM table1
WHERE cal_year <= EXTRACT(YEAR FROM SYSDATE)
ORDER BY cal_year DESC
FETCH FIRST ROW WITH TIES;

Answer 3

Optionally (if you're on a database version which doesn't support FETCH FIRST ROW WITH TIES Thorsten suggested):
with year 2021 in the table:
SQL> select * from table1
2 where cal_year = case when (select max(1) from table1
3 where exists (select null from table1
4 where cal_year = to_char(sysdate, 'yyyy')
5 )
6 ) = 1 then to_char(sysdate, 'yyyy')
7 else to_char(add_months(sysdate, -12), 'yyyy')
8 end;
CAL_ N
---- -
2021 E
2021 F
Without this year:
SQL> delete from table1 where cal_year = 2021;
2 rows deleted.
SQL>
SQL> select * from table1
2 where cal_year = case when (select max(1) from table1
3 where exists (select null from table1
4 where cal_year = to_char(sysdate, 'yyyy')
5 )
6 ) = 1 then to_char(sysdate, 'yyyy')
7 else to_char(add_months(sysdate, -12), 'yyyy')
8 end;
CAL_ N
---- -
2020 A
2020 B
2020 C
2020 D
SQL>
What does it do?
lines #2 - 5: SELECT* (within CASE) returns 1 if EXISTS says that there's at least one row whose CAL_YEAR = this year
if that's so (i.e. 1 has been returned), then CAL_YEAR is compared to this year (to_char(sysdate, 'yyyy'))
otherwise, if SELECT returns something else (most probably NULL), CAL_YEAR is compared to previous year (that's what to_char(add_months(sysdate, -12), 'yyyy') does - subtracts 12 months from today's date and extracts year from it)