Conditional querying based on the current date & time - sql

Question

I have an sql query in which I need to select the records from table where the time is between 3:00 PM yesterday to 3:00 PM today if today's time is more than 3:00 PM.
If today's time is less than that, like if today's time is 1:00 PM. then then my query should take today's time as 1:00 PM (which should return me records).
I need to get the time between 3:00pm yesterday to 3:00pm today if todays time is more than 3:00pm
if todays time is less than 3:00pm then get the 3:00pm yesterday to current time today

Answer 1

The best way of handling this is to use an IF statement:
IF TO_CHAR(SYSDATE, 'HH24') >= 15 THEN
SELECT x.*
FROM YOUR_TABLE x
WHERE x.date_column BETWEEN TO_DATE(TO_CHAR(SYSDATE -1, 'YYYY-MM-DD')|| ' 15:00:00', 'YYYY-MM-DD HH24:MI:SS')
AND TO_DATE(TO_CHAR(SYSDATE, 'YYYY-MM-DD')|| ' 15:00:00', 'YYYY-MM-DD HH24:MI:SS')
ELSE
SELECT x.*
FROM YOUR_TABLE x
WHERE x.date_column BETWEEN TO_DATE(TO_CHAR(SYSDATE -1, 'YYYY-MM-DD')|| ' 15:00:00', 'YYYY-MM-DD HH24:MI:SS')
AND SYSDATE
END IF;
Conditional WHERE clauses are non-sargable.
Previously:
If I understand correctly, you want to get records within the last day. If the current time is 3 PM or later, the time should be set to 3 PM. If earlier than 3 PM, take the current time...
SELECT x.*
FROM YOUR_TABLE x
JOIN (SELECT CASE
WHEN TO_CHAR(SYSDATE, 'HH24') >= 15 THEN
TO_DATE(TO_CHAR(SYSDATE, 'YYYY-MM-DD')|| ' 15:00:00', 'YYYY-MM-DD HH24:MI:SS')
ELSE SYSDATE
END AS dt
FROM DUAL) y ON x.date_column BETWEEN dt - 1 AND dt
Note:
dt - 1 means that 24 hours will be subtracted from the Oracle DATE.
Reference:
TO_CHAR
TO_DATE

Answer 2

There is no need for an IF statement. This can be solved easily with simple SQL.
My table T23 has some records with dates; here is a sample with times at 3.00pm:
SQL> select id, some_date from t23
2 where to_char(some_date,'HH24') = '15'
3 /
ID SOME_DATE
---------- ---------
14 16-MAY-11
38 17-MAY-11
62 18-MAY-11
81 19-MAY-11
SQL>
As the current time is before 3.00pm my query will return records from 17-MAY and 18-MAY but not the record where ID=62...
SQL> select to_char(sysdate, 'DD-MON-YYYY HH24:MI') as time_now
2 from dual
3 /
TIME_NOW
-----------------
18-MAY-2011 10:45
SQL> select id, to_char(some_date, 'DD-MON-YYYY HH24:MI') as dt
2 from t23
3 where some_date between trunc(sysdate-1)+(15/24)
4 and least( trunc(sysdate)+(15/24), sysdate)
5 /
ID DT
---------- -----------------
38 17-MAY-2011 15:00
39 17-MAY-2011 16:00
40 17-MAY-2011 17:00
41 17-MAY-2011 18:00
42 17-MAY-2011 19:00
43 17-MAY-2011 20:00
44 17-MAY-2011 21:00
45 17-MAY-2011 22:00
46 17-MAY-2011 23:00
47 18-MAY-2011 00:00
48 18-MAY-2011 01:00
49 18-MAY-2011 02:00
50 18-MAY-2011 03:00
51 18-MAY-2011 04:00
52 18-MAY-2011 05:00
53 18-MAY-2011 06:00
54 18-MAY-2011 07:00
55 18-MAY-2011 08:00
56 18-MAY-2011 09:00
57 18-MAY-2011 10:00
20 rows selected.
SQL>