Fetch distinct available dates from table - mysql

Question

I have a data table where data is present for every date (for 50 branches) except saturday and sunday. I am trying to get the last valid date from table from multiple given dates.
select distinct BW_DATE from backdated_weekly where BW_DATE <='2021-09-30' or BW_DATE<='2021-09-26' order by BW_DATE desc;
As 2021-09-30 is a valid date but 2021-09-26 (Sunday) is not present in table. I am trying to get output as
2021-09-30
2021-09-24
But above query gives all results below given dates.

Answer 1

If it is confirmed there are dates continuously in the table for all mon-fri only, simply select the maximum date up to the given date
SELECT MAX(BW_DATE)
FROM backdated_weekly
WHERE BW_DATE <= '2021-09-30'
UNION
SELECT MAX(BW_DATE)
FROM backdated_weekly
WHERE BW_DATE <= '2021-09-26'
Also we can calculate newest date in mon-fri for a given date directly without any table
WEEKDAY is the function to be used
Returns the weekday index for date (0 = Monday, 1 = Tuesday, … 6 =
Sunday).
SELECT CASE WHEN WEEKDAY('2021-09-30') IN ( 5, 6 ) THEN DATE('2021-09-30') - INTERVAL WEEKDAY('2021-09-30') - 4 DAY ELSE DATE('2021-09-30') END
UNION
SELECT CASE WHEN WEEKDAY('2021-09-26') IN ( 5, 6 ) THEN DATE('2021-09-26') - INTERVAL WEEKDAY('2021-09-26') - 4 DAY ELSE DATE('2021-09-26') END
https://dbfiddle.uk/?rdbms=mysql_8.0&fiddle=477775c0eddbfa733e60bc629a8a68d4