Date function on oracle
-
19-12-2020 - |
题
I've got a question about date function on oracle.
I have the following table
statistic_table(
pages AS varchar(10),
date_created AS date
);
I have the following sql
SELECT COUNT(*) FROM statistic_table WHERE date_created BETWEEN sysdate-5 AND sysdate-1
and
SELECT COUNT(*) FROM statistic_table WHERE date_created BETWEEN to_date('12-AUG-2011') AND to_date('16-AUG-2011');
the question is, why is it return different numbers. assuming sysdate-5 returns 12-aug-2011 and sysdate-1 returns 16-aug-2011
Any help would be much appreciated!
Cheers,
解决方案
A date in Oracle is a point in time with a precision of a second.
SYSDATE
returns the current date and time and is therefore not the same as to_date('17-AUG-2011')
:
SQL> SELECT to_char(sysdate, 'dd-mon-yyyy hh24:mi:ss') FROM DUAL;
TO_CHAR(SYSDATE,'DD-MON-YYYYHH
------------------------------
17-aug-2011 15:52:13
Use the TRUNC
function if you only want the date component:
SQL> SELECT to_char(trunc(sysdate), 'dd-mon-yyyy hh24:mi:ss') FROM DUAL;
TO_CHAR(TRUNC(SYSDATE),'DD-MON
------------------------------
17-aou-2011 00:00:00
其他提示
sysdate - 5 will give you a date with the current time. So if I ran it at 1pm precisely, the query would be equivalent to:
select (*)
FROM statistic_table
WHERE date_created BETWEEN to_date('12-Aug-2011 13:00:00')
AND to_date('16-Aug-2011 13:00:00')
whereas the second query is:
select (*)
FROM statistic_table
WHERE date_created BETWEEN to_date('12-Aug-2011 00:00:00')
AND to_date('16-Aug-2011 00:00:00')
you should probably try this instead:
select (*)
FROM statistic_table
WHERE date_created BETWEEN trunc(sysdate) -5
AND trunc(sysdate) -1
Because SYSDATE includes a time component, so if the current time is 11:22:33, then
SELECT COUNT(*) FROM statistic_table
WHERE date_created BETWEEN sysdate-5 AND sysdate-1
is actually equivalent to
SELECT COUNT(*) FROM statistic_table
WHERE date_created BETWEEN to_date('12-AUG-2011 11:22:33','DD-MON-YYYY HH24:MI:SS')
AND to_date('16-AUG-2011 11:22:33','DD-MON-YYYY HH24:MI:SS')
To avoid the time component do this:
SELECT COUNT(*) FROM statistic_table
WHERE date_created BETWEEN TRUNC(sysdate)-5 AND TRUNC(sysdate)-1
An Oracle DATE
always has a day and a time component.
sysdate-5
returns a date exactly 5 days ago. If today is August 17 at 10 AM, for example, sysdate-5
returns August 12 at 10 AM.
to_date('12-AUG-2011', 'DD-MON-YYYY')
, on the other hand, returns August 12 at midnight. So it returns a date that is 10 hours earlier than sysdate-5
.
sysdate auto returns with a time component as mentioned by the previous answers.
When using to_date it is converting a string to a date. With this being said you can pass in parameters to make it return the same thing.
Have a look at this link that explains it.