SQL check day of week - sql

Question

How to check if it's a weekend in SQL?
I know I can convert sysdate to a number using this
SQL> select to_char(sysdate, 'd') from dual;
TO_CHAR(SYSDATE,'D')
But I'm not really sure how to check if today is a 6 or 7.

Answer 1

Do not use TO_CHAR with the D format model for this as it is dependant on the NLS_TERRITORY session parameter.
For example, when SYSDATE = 2018-09-10 (a Monday):
ALTER SESSION SET NLS_TERRITORY = 'France';
SELECT TO_CHAR( SYSDATE, 'D' ) FROM DUAL;
Outputs 1 but the same query in a different territory:
ALTER SESSION SET NLS_TERRITORY = 'America';
SELECT TO_CHAR( SYSDATE, 'D' ) FROM DUAL;
Outputs 2.
Instead, you can use TRUNC and the IW format model:
SELECT TRUNC( SYSDATE ) - TRUNC( SYSDATE, 'IW' ) FROM DUAL
Outputs 0 for Monday (and 1 for Tuesday ... 6 for Sunday) and is independent of the NLS_TERRITORY setting.
So you could filter this to give weekends as:
SELECT *
FROM DUAL
WHERE TRUNC( SYSDATE ) - TRUNC( SYSDATE, 'IW' ) IN ( 5, 6 )
or
SELECT *
FROM DUAL
WHERE SYSDATE - TRUNC( SYSDATE, 'IW' ) >= 5
If you want the days 1-indexed for consistency with your expected output from TO_CHAR (rather then 0-indexed) then just add 1 to the value.

Answer 2

sysdate is a pseudo column. You don't need to query it, you can evaluate it directly:
IF TO_CHAR(SYSDATE, 'D') IN ('6', '7') THEN
-- Do something
END IF;

Answer 3

I would avoid the ambiguous 'D' format as this varies between territories (the week starts after the weekend where I live), and use
if to_char(sysdate,'fmDY','nls_date_language=English') like 'S%'
then
Regarding the 'D' format, unfortunately to_char doesn't let you specify nls_territory inline, so without an explicit alter session command, it will rely on the session settings at runtime. I've seen production bugs due to this, where the same code worked in London but failed in New York.

Answer 4

And here's the logic in a reusable function, but flipped to ask "Is it a weekday?" (not a weekend). You could add a parameter for the start day of the weekdays (2 is the default in Oracle; Sunday is day #1).
CREATE OR REPLACE FUNCTION is_weekday (date_in IN DATE)
RETURN BOOLEAN
IS
BEGIN
RETURN TO_CHAR (date_in, 'D') BETWEEN 2 AND 6;
END;
/
DECLARE
l_date DATE := DATE '2018-09-10';
BEGIN
DBMS_OUTPUT.put_line ('If your weekend is Saturday and Sunday....');
FOR indx IN 1 .. 7
LOOP
DBMS_OUTPUT.put_line (
TO_CHAR (l_date, 'FMDay, Month DD YYYY')
|| ' is '
|| CASE WHEN NOT is_weekday (l_date) THEN 'not ' END
|| 'a weekday');
l_date := l_date + 1;
END LOOP;
END;
/
Try it in LiveSQL:
https://livesql.oracle.com/apex/livesql/file/content_G8NQSY6NP48NPJX96RLQ51SUE.html