Here are some quick and dirty examples for adding and subtracting days and months and finding the difference between dates in Oracle.

These examples select the result from the ‘dual’ table. Dual is a dummy table that exists in all Oracle databases. I am also using sysdate heavily. Sysdate simply returns the current date and time.

Adjusting Days, Weeks, Hours and Minutes

To add and subtract days from a date we simply use + or -. Here are some examples:

SQL> SELECT sysdate + 7 FROM dual;

SYSDATE+7
---------
06-DEC-05

SQL> SELECT sysdate - 30 FROM dual;

SYSDATE-3
---------
30-OCT-05

SQL> SELECT to_char(sysdate - 14, 'MM/DD/YYYY HH:MI AM') FROM dual;

TO_CHAR(SYSDATE-14,
-------------------
11/15/2005 09:41 AM

In the first example we see that the query returns 7 days from today. The second one shows 30 days before today. In the third query I have added the to_char function so we see hour and minute. This shows us that while the date has changed, the time has not.

The first and third examples above also show how adding days would be used to add weeks. If you wanted to simplify this you could add the logic into the query like this:

SQL> SELECT sysdate + (7 * 2) FROM dual;

SYSDATE+(
---------
13-DEC-05

Likewise to work with hours you would use fractional days. The simplest way to show this is by dividing the hours by 24 right in the query. The parentheses may not be necessary, but I feel they make the query a little clearer.

Here I show the current time, then the current time plus two hours:

SQL> SELECT to_char(sysdate, 'HH:MI AM') FROM dual;

TO_CHAR(
--------
09:48 AM

SQL> SELECT to_char(sysdate + (2/24), 'HH:MI AM') FROM dual;

TO_CHAR(
--------
11:48 AM

An alternative to this method is to use the numtodsinterval function. The example above can instead be written like this:

SQL> SELECT
to_char(sysdate + numtodsinterval(2, 'HOUR'), 'HH:MI AM')
FROM dual;

TO_CHAR(
--------
11:57 AM

Here the numtodsinterval function is doing the work of dividing 2/24 for hours. Valid options for the numtodsinterval are ‘DAY’, ‘HOUR’, ‘MINUTE’, or ‘SECOND’. Here is an example using ‘MINUTE’. When working with minutes the numtodsinterval function is much more readable.

SQL> SELECT
to_char(sysdate + numtodsinterval(45, 'MINUTE'), 'HH:MI AM')
FROM dual;

TO_CHAR(
--------
10:47 AM

Adjusting Months and Years

To work with months and years (either of which may have a varying number of days) Oracle has provided the function numtoyminterval. This works much like the numtodsinterval function mentioned above by taking a number and a string. Valid options for the string are ‘YEAR’ or ‘MONTH’.

SQL> SELECT
to_char(sysdate + numtoyminterval(5, 'MONTH'), 'MM/DD/YYYY')
FROM dual;

TO_CHAR(SY
----------
04/29/2006

SQL> SELECT
to_char(sysdate + numtoyminterval(2, 'YEAR'), 'MM/DD/YYYY')
FROM dual;

TO_CHAR(SY
----------
11/29/2007

Comparing dates

Let’s say we want to compare some dates and find out how many days or weeks between them. To simply see the result in days we can use the minus operator like this:

SQL> SELECT
TO_DATE('12/25/2005', 'MM/DD/YYYY') - sysdate
FROM dual;

TO_DATE('12/25/2005','MM/DD/YYYY')-SYSDATE
------------------------------------------
26.5124421

The result is expressed in days including fractional hours. Of course if we wanted weeks we could just divide by 7. Similarly if we’re looking for hours we could multiply by 24, but if we want months we need to use the months_between function.

SQL> SELECT
months_between(sysdate, to_date('01/01/2006', 'MM/DD/YYYY'))
FROM dual;

MONTHS_BETWEEN(SYSDATE,TO_DATE('01/01/2006','MM/DD/YYYY'))
----------------------------------------------------------
-1.0829409

Finding the Latest or Earliest Date in a Set

The Oracle functions greatest and least can be used on dates to return the latest or earliest date.

SQL> SELECT
greatest(sysdate, to_date('09/11/2005','MM/DD/YYYY'),
to_date('12/25/2005','MM/DD/YYYY'))
FROM dual;

GREATEST(
---------
25-DEC-05

SQL> SELECT
least(sysdate, to_date('09/11/2005','MM/DD/YYYY'),
to_date('12/25/2005','MM/DD/YYYY'))
FROM dual;

LEAST(SYS
---------
11-SEP-05

What’s the Last Day in a Given Month

The last_day function can be used to return the last day in a given month.

SQL> select last_day(sysdate) from dual;

LAST_DAY(
---------
30-NOV-05

Next Day of the Week After a Date

The next_day function gives the date of the next occurrence of a day of the week (‘Monday’, ‘Tuesday’, etc.) after a given date. Here we see the date of the next Sunday after today:

SQL> select next_day(sysdate,'Sunday') from dual;

NEXT_DAY(
---------
04-DEC-05

Still haven’t found what you’re looking for?

You may also want to look at these other articles:

Converting Time Zones in Oracle
Oracle, SQL, Dates and Timestamps
UNIX timestamp to Oracle Date Conversion

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Don’t just grow your TEMP tablespace, examine it!

Recently I was facing a problem not unusual in high-throughput Oracle databases… a full TEMP tablespace. I’ve run into this before and it can be frustrating trying to determine where all the space went. In this case we are using a 6 gig temporary tablespace and for some reason it was full.

Well, all the gorey details aside, one thing that helped me determine what was going on was this tip from Oracle which contains code to examine who is using your temporary tablespace up.

By running the following command (reprinted here for easy reference and because there are nasty line breaks on Oracle’s site) you get a fairly good idea of the usage of temporary space by tablespace, username and amount used.

set pagesize 10000
set linesize 133
column tablespace format a15 heading 'Tablespace Name'
column segfile# format 9,999 heading 'File|ID'
column spid format 9,999 heading 'Unix|ID'
column segblk# format 999,999,999 heading 'Block|ID'
column size_mb format 999,999,990.00 heading "Mbytes|Used"
column username format a15
column program format a15

select b.tablespace, b.segfile#, b.segblk#,
round(((b.blocks*p.value)/1024/1024),2) size_mb,
a.sid, a.serial#, a.username, a.osuser, a.program, a.status
from v$session a, v$sort_usage b, v$process c, v$parameter p
where p.name='db_block_size' and a.saddr = b.session_addr
and a.paddr=c.addr
order by b.tablespace,b.segfile#,b.segblk#,b.blocks;

While I consider rewriting this into a somewhat more palatable form, on the occasion that I need this I don’t typically care about nice formatting… I just want the numbers in a hurry.

To clear up unused TEMP space Oracle also recommends running this as sysdba:

alter tablespace temp default storage(pctincrease 0);

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What are the valid characters for Oracle passwords? This is a more complicated question than you would think. Here are the basic restrictions on Oracle passwords. I believe these apply to all (8i or later) Oracle database versions; however I did these examples in a 10gR2 instance.

First the rules:

Passwords can be from 1 to 30 characters.

The first character in an Oracle password must be a letter.

Only letters, numbers, and the symbols “#”, “_” and “$” are acceptable in a password.

Examples:

SQL> alter user jemmons identified by abc123;

User altered.

SQL> alter user jemmons identified by 123abc;
alter user jemmons identified by 123abc
*
ERROR at line 1:
ORA-00988: missing or invalid password(s)

SQL> alter user jemmons identified by abc!123;
alter user jemmons identified by abc!123
*
ERROR at line 1:
ORA-00922: missing or invalid option

In the first example we see a password that meets all the rules. The second password starts with a number and therefore fails. The third example contains the special character “!” and fails.

Now the exception:

By placing double quotes around a password you can use most standard ASCII characters in a password.

Examples:

SQL> alter user jemmons identified by "123abc";

User altered.

SQL> connect jemmons/123abc;
Connected.
SQL> alter user jemmons identified by "abc!123";

User altered.

SQL> connect jemmons/abc!123;
Connected.

We see that the quotes let us work around some of these restrictions. This is useful if you are working in a fairly simple environment, however if it is possible that a user’s password could be changed by means which you do not control it is likely doing this would cause more confusion than it would solve.

It is also worth note that capitalization is not considered when storing Oracle passwords. Here’s an example:

SQL> alter user jemmons identified by ABC123;

User altered.

SQL> connect jemmons/abc123;
Connected.

Before the password is encrypted into the database it is put in all caps. When you enter a password for authentication it is capitalized so it can be compared against the stored encrypted password.

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With Oracle 10g there has been a small but useful change made to Oracle’s Optimal Flexible Architecture.

The Optimal Flexible Architecture standards are a guideline for setting up Oracle databases to minimize downtime and maximize scalability. For more information, check out my article on OFA.

In 10g, Oracle has added one level to the ORACLE_HOME path. An Oracle home directory which was formerly /u01/app/oracle/product/9.2.0 is now one more level deeper at /u01/app/oracle/product/10g/db_1.

By adding install type and an install number as the final level of the Oracle home variable it is now possible to have two or more installs of the same version of Oracle in the same Oracle directory.

Oracle offers up the idea of using db_1, db_2 and so-on for full database releases and client_1, client_2 and so-on for client installs I can also see using this method to install Oracle applications servers in the same directory as well.

To read more about OFA, check out my earlier article on the topic and Oracle’s explanation of OFA.

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No Oracle geek should be without one of these.

If you’ve been an Oracle DBA for long you know the horrors of navigating through Oracle’s “data dictionary”, the tables and views which contain all the metadata about your database. While views like dba_objects and dba_tab_privs are their own level of hell, one thing is certain… the v$ views are far worse.

While the names of the v$ views are not terrible in themselves (e.g. v$session, v$datafile, v$tablespace) the true crux of the problem is you never use them. Any time your database is running fine, you would go to the dba_ tables and the like. Only when your database refuses to open after a fairly nasty crash and users are knocking on your door asking when you will have the database up do you finally need the v$ views, and then you can’t remember any of them.

v$viewsEnter tusc.com. I’m not sure how long they have been doing this, but they offer a free poster of the Oracle v$ views. I’ve seen these as far back as Oracle 8.0, and the company has been around since 1988, so clearly they know what they’re doing.

Well, they seem to be a little confused about “free”, but basically they want eight bucks to send you one of these and two bucks for each additional one. I figure they’re not making any money on this, just covering shipping and handling (and not in the same way eBay-ers need $50 to cover shipping and handling so they can sell something for cheap).

Still not convinced? Tusc has also been nice enough to offer the poster in PDF format. Download it, check it out, put it somewhere and forget about it until you have a database misbehaving then go frantically after it.

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