SQL SYSDATE tips
Oracle Tips by Burleson Consulting
Question: I need
to understand how to add a data into my
Oracle database with the SQL SYSDATE
function. Can you show an example
of using SYSDATE with SQL?
One of the confounding problems
with Oracle SQL is the SYSDATE
The purpose of SYSDATE is simply to
return the current date and time associated with the OS on which the
database in question resides. The returned value of SYSDATE is of the
datatype: DATE. The format of the value returned by SYSDATE is
determined by the nls_date_format initialization parameter.
- See here for the
nls_date_format parameters for SYSDATE
- See here for
hate math manipulation with SQL SYSDATE
When using distributed SQL statements, the SYSDATE function returns the
date and time that are set for the operating system of the local database.
SYSDATE cannot be used in the condition statement of a CHECK constraint.
Oracle SYSDATE functions can be
used to convert into elapsed timeand place the
SYSDATE value inside an
SQL> select sysdate-(sysdate-3)
Here we see that elapsed times
are expressed in days.
Hence, we can use easy
conversion functions to convert
this to hours or minutes.
However, when the minutes are
not a whole number, we have the
problem of trailing decimal
course, we can overcome this
with the ROUND function with
Oracle SYSDATE, remembering that
we must first convert the DATE
datatype to a NUMBER type:
can use these Oracle SYSDATE
functions to convert an elapsed
time into rounded elapsed
minutes, and place the value
inside an Oracle table. In
this example, we have a Oracle
logoff system-level trigger that
computes the elapsed session
time and places it inside a
Oracle STATSPACK user_log
Dates and SQL SYSDATE
Dates are stored in the database as large numbers. The
actual size of the data number is dependent on the operating system
supporting the database. When a date is requested, it is returned in a
human readable form.
When date values are compared in the where
clause, the format of the date must match the format that the database is
using or the comparison will fail. Alternately, if you are using another
format, then you must tell the database how your date is formatted. The
default format that the Oracle database uses is: DD-Mon-YY. This is how
SQL*Plus will show you the data, when requested. So, how do I reformat the
date returned? We will cover date functions in single row functions in
To get the current date, you select from a function
called SYSDATE. SYSDATE returns the current date from the server operating
system supporting the database.
SQL> SELECT SYSDATE
The dual table is a pseudo-table that allows you to
execute functions that require selecting from a table.
Lastly, because a date is stored in the database as a
number, you can perform date math.
3 SYSDATE - 1 Yesterday,
4 SYSDATE + 1 Tomorrow
--------- --------- ---------
23-JAN-05 22-JAN-05 24-JAN-05
As you can see, the standard unit in date math is one
day. When you add time to the date with SQL updates, you do it in fractions
of a day.
1 Day 1 1 1
Hour 1/24 1/24 0.0417
1 Min 1/(24x60) 1/1440 .000694
1 Sec 1/(24x60x60)
The notation in the second column is most commonly
used, because it is so much easier to read. Five minutes is 5/(24x60), much
easier than 5/1440 or .00347. When we get to date functions in Chapter 2,
you will see that there are functions to do date math by months, weeks and