Using variables in Oracle SQL

Question

I'm not much experienced with Oracle SQL and been trying to accomplish some task for which I intend to use

select count(*) from TABLE where date = (select trunc(sysdate -1 ) from dual) 

The above query gives me the result for all the records with sysdate minus 1. I want to automate it to handle the scenario of Sat and Sunday and modify the query to something like below

select count(*) from TABLE where date = (select trunc(sysdate -@var ) from dual)

where @var = 2 if the query runs on Sunday and @var = 3 if the query is running on Monday

Answer 1

TRUNC( SYSDATE, 'IW' ) will truncate the date to the start of the ISO week - so midnight Monday. TRUNC( SYSDATE ) - TRUNC( SYSDATE, 'IW' ) will give the number of full days since the start of the ISO week (Monday = 0, Tuesday = 1, ... Sunday = 6) and you can just put that into a CASE statement:

select count(*)
from   your_table
where  date_col = TRUNC(SYSDATE) - CASE TRUNC(SYSDATE) - TRUNC(SYSDATE, 'IW')
                                   WHEN 0 THEN 3 -- Monday
                                   WHEN 6 THEN 2 -- Sunday
                                          ELSE 1 -- Other days
                                   END