I have a datetime column.
I want two columns: a date and a time column.
How can I split my column into two?
Use:
a DATE data-type with the time component set to midnight for the date (you can enforce this with a check constraint); and
an INTERVAL DAY(0) TO SECOND data-type for the time component.
CREATE TABLE table_name(
datetime_column DATE,
date_column DATE,
time_column INTERVAL DAY(0) TO SECOND,
CONSTRAINT table_name__date_column__chk CHECK (date_column = TRUNC(date_column))
)
If you want to get the combined date-time then you can easily add the two to get back to a date-time value.
How can I split my column into two?
Assuming you have the columns you can use:
UPDATE table_name
SET date_column = TRUNC(datetime_column),
time_column = (datetime_column - TRUNC(datetime_column)) DAY TO SECOND;
db<>fiddle here
As Gordon commented, there's no time datatype in Oracle.
Though, literally answering what you asked, you can separate date and time and store each of them into their own columns - it's just that these will be VARCHAR2 columns and you can only look at how pretty they are. You can't, for example, do any date arithmetic on them; first you'd have to convert them back to date datatype, so question is what you really want to do with what you get.
Anyway, here you are:
SQL> create table test
2 (datum date,
3 date_only varchar2(10),
4 time_only varchar2(8)
5 );
Table created.
Sample value:
SQL> insert into test (datum) values (sysdate);
1 row created.
Split date to two parts:
SQL> update test set
2 date_only = to_char(datum, 'dd.mm.yyyy'),
3 time_only = to_char(datum, 'hh24:mi:ss');
1 row updated.
What's in there?
SQL> alter session set nls_date_format = 'dd.mm.yyyy hh24:mi:ss';
Session altered.
SQL> select * from test;
DATUM DATE_ONLY TIME_ONL
------------------- ---------- --------
05.08.2021 21:05:06 05.08.2021 21:05:06
SQL>
Since there is no specific datatype for time, here my suggestion would be to keep the datetime in main column and add two VIRTUAL COLUMN for date value and time value respectively.
Oracle 11g has introduced a new feature that allows you to create a VIRTUAL COLUMN, an empty column that contains a function upon other table columns (the function itself is stored in the data dictionary).
However, it all depends on what you are going to do with it.
Please elaborate your requirement so that you will get a more specific answer.
Here is the table
create table call(
id varchar(5),
start_time timestamp,
end_time timestamp,
duration INTERVAL DAY(5) TO SECOND(3),
primary key(id)
);
And the trigger:
create or replace TRIGGER DURATION
BEFORE INSERT ON call
for each row
BEGIN
select end_time - start_time into :new.duration from dual;
END;
so that it could work like this when doing insertion
insert into call values(111,'2015-04-21 15:42:23','2016-11-03 18:32:47',null);
It's saying that the end_time is invalid identifier. I do realize I might need a sequence or something to make the end_time be referred to the specific row I am inserting, but I am not sure what to put there.
I would try this change for the timestamp calculation:
select :new.end_time - :new.start_time into :new.duration from dual;
I suspect that qualifying the end_time and start_time columns as coming from the :new row may be necessary to do this correctly.
One additional point is that the INSERT statement should probably include the column names associated with the values. This should also allow you to omit the 'duration', since it's specifically calculated in this trigger.
Consider this instead:
insert into call (id, start_time, end_time) values(111,'2015-04-21 15:42:23','2016-11-03 18:32:47');
Hard lessons learned after making schema updates that suddenly break INSERT statements that had previously worked. Worse, sometimes the INSERT doesn't actually fail, but silently goes about doing the wrong thing.
Small entry level question with Oracle 10 SQL. I'm creating a table with a column with a "date" type which is supposed to hold values looking like this : "00:00". I have a constraint with checks the time to be between 00:00 and 23:00.
Now, what I can't quite grasp is how to approach the problem. I do feel like I'm missing something quite basic but I can't quite figure out what...
Do I :
1) Extract and check the date inside my constraint? If so, is there a way to do that? Can I insert data looking like this : TO_DATE('13-AUG-66 12:56','DD-MON-YY HH:MI'), and use some kind of "Extract" function inside my constraint?
2) The exercise in question does mention the date type for that particular column. By default, I assume that it doesn't hold hours and needs to be modified using alter_session?
A constraint only enforces a restriction. It cannot modify data. A BEFORE INSERT trigger can modify data but is generally less efficient than a constraint.
If you want to create a constraint that ensures that the time component is always midnight
CREATE TABLE table_name (
col DATE CHECK( col1 = TRUNC( col ))
);
If you want to create a trigger that modifies the data
CREATE OR REPLACE TRIGGER trg_trunc_dt
BEFORE INSERT ON table_name
FOR EACH ROW
BEGIN
:new.date_column := TRUNC( :new.date_column );
END;
A DATE always contains a day and a time component. Your client may or may not display either component. Many clients will use implicit data type conversion in which case the session's NLS_DATE_FORMAT controls how a DATE is converted to a VARCHAR2 and what elements are incorporated into the string.
A date type always has a date part and a time part. It is just a value and has thus no formatting. If you display a time as 22:50 or 10:50pm for example is up to you. You either rely on your settings with to_char(mydate) or specify a format to_char(mydate,'hh24:mi').
This said, you can simply use the time part of your column and ignore the date part. If you want to avoid confusion about different dates being stored, you can use a trigger setting the date part to 01.01.0001 for instance:
create or replace Trigger trg_datetable_datepart
before insert or update of mydate on datetable
for each row
begin
:new.mydate := to_date( '01.01.0001 ' || to_char(:new.mydate, 'hh24:mi') , 'dd.mm.yyyy hh24:mi' );
end;
To avoid inserts of times after 23h you would write a check constraint:
alter table datetable add constraint check_datetable_timepart check ( to_char(mydate, 'hh24:mi') <= '23:00' );
Bakground:
I've got a legacy app I'm working on that uses DATE types for most time storage in the database. I'd like to try update some of these tables so that they can utilize time zones since this is causing problems with users in different areas from where the db is(see A below). This is for Oracle 10g.
Quetions:
1) Can I migrate this "in place." That is can I convert like so
DATE_COL = type:DATE => DATE_COL = type:TIMESTAMP
...or will I have to use a different column name?
Keep in mind that data needs to be retained. If this can be done semi-easily in a migration script it will work for my purposes.
2) Will this type of conversion be backwards compatible? We likely have some scripts or reports that will hit this table that we may not know about. We can probably deal with it but I'd like to know what sort of hornet's nest I'm walking into.
3) What pitfalls should I be on the lookout for?
Thanks,
EDIT:
(partly in response to Gary)
I'm fine with a multi-step process.
1) move data to a new Timestamp column (caled TEMP) with some sort of conversion
2) drop old column (we'll call it MY_DATE)
3) create new timestamp column with the old date column name (MY_DATE)
4) move data to the MY_DATE column
5) drop TEMP column
A Gary also wanted clarification on the specific timezone issue. I copied my answer from below to keep it more readable.
Basically the data will be accessed from several different areas. We need to be able to convert to/from the local time zone as needed. We also have triggers that use sysdate further complicating things. timestamp with time zone alleviates a lot of this pain.
Oh and thanks for the answers so far.
You could just run:
ALTER TABLE your_table MODIFY your_date_column TIMESTAMP WITH TIME ZONE;
But I would recommend adding a TIMESTAMP column to the table, using an UPDATE statement to populate, and drop the original date column if you so choose:
ALTER TABLE your_table ADD date_as_timestamp TIMESTAMP WITH TIME ZONE;
UPDATE your_table
SET date_as_timestamp = CAST(date_column AS TIMESTAMP WITH TIME ZONE);
The conversion is backwards compatible - you can switch back & forth as you like.
Simple enough to demonstrate
SQL> create table x (y date);
Table created.
SQL> insert into x select sysdate from dual;
1 row created.
SQL> commit;
Commit complete.
SQL> alter table x modify y timestamp;
Table altered.
SQL> select * from x;
Y
---------------------------------------------------------------------------
03/NOV/09 12:49:03.000000 PM
SQL> alter table x modify y date;
Table altered.
SQL> select * from x;
Y
---------
03/NOV/09
SQL> alter table x modify y timestamp with time zone;
alter table x modify y timestamp with time zone
ERROR at line 1:
ORA-01439: column to be modified must be empty to change datatype
SQL> alter table x modify y timestamp with local time zone;
Table altered.
SQL> alter table x modify y date;
Table altered.
So you can go from date to timestamp (or timestamp with local timezone) and back again, but not for timestamp with time zone (ie where the offset is persisted).
You'd have to add another column, and copy the existing data over (with a default for the appropriate time zone).
"causing problems with users in different areas from where the db is".
Might help to be a bit more specific. Is it sufficient to convert the dates (or timestamps) from the database timezone to the user's timezone when inserted/changed/queried, or do you actually need to persist the fact that the record was created at 3:00pm in a specific timezone.
I have a sqlite (v3) table with this column definition:
"timestamp" DATETIME DEFAULT CURRENT_TIMESTAMP
The server that this database lives on is in the CST time zone. When I insert into my table without including the timestamp column, sqlite automatically populates that field with the current timestamp in GMT, not CST.
Is there a way to modify my insert statement to force the stored timestamp to be in CST? On the other hand, it is probably better to store it in GMT (in case the database gets moved to a different timezone, for example), so is there a way I can modify my select SQL to convert the stored timestamp to CST when I extract it from the table?
I found on the sqlite documentation (https://www.sqlite.org/lang_datefunc.html) this text:
Compute the date and time given a unix
timestamp 1092941466, and compensate
for your local timezone.
SELECT datetime(1092941466, 'unixepoch', 'localtime');
That didn't look like it fit my needs, so I tried changing the "datetime" function around a bit, and wound up with this:
select datetime(timestamp, 'localtime')
That seems to work - is that the correct way to convert for your timezone, or is there a better way to do this?
simply use local time as the default:
CREATE TABLE whatever(
....
timestamp DATE DEFAULT (datetime('now','localtime')),
...
);
You should, as a rule, leave timestamps in the database in GMT, and only convert them to/from local time on input/output, when you can convert them to the user's (not server's) local timestamp.
It would be nice if you could do the following:
SELECT DATETIME(col, 'PDT')
...to output the timestamp for a user on Pacific Daylight Time. Unfortunately, that doesn't work. According to this SQLite tutorial, however (scroll down to "Other Date and Time Commands"), you can ask for the time, and then apply an offset (in hours) at the same time. So, if you do know the user's timezone offset, you're good.
Doesn't deal with daylight saving rules, though...
In the (admitted rare) case that a local datatime is wanted (I, for example, store local time in one of my database since all I care is what time in the day is was and I don't keep track of where I was in term of time zones...), you can define the column as
"timestamp" TEXT DEFAULT (strftime('%Y-%m-%dT%H:%M','now', 'localtime'))
The %Y-%m-%dT%H:%M part is of course optional; it is just how I like my time to be stored. [Also, if my impression is correct, there is no "DATETIME" datatype in sqlite, so it does not really matter whether TEXT or DATETIME is used as data type in column declaration.]
When having a column defined with "NOT NULL DEFAULT CURRENT_TIMESTAMP," inserted records will always get set with UTC/GMT time.
Here's what I did to avoid having to include the time in my INSERT/UPDATE statements:
--Create a table having a CURRENT_TIMESTAMP:
CREATE TABLE FOOBAR (
RECORD_NO INTEGER NOT NULL,
TO_STORE INTEGER,
UPC CHAR(30),
QTY DECIMAL(15,4),
EID CHAR(16),
RECORD_TIME NOT NULL DEFAULT CURRENT_TIMESTAMP)
--Create before update and after insert triggers:
CREATE TRIGGER UPDATE_FOOBAR BEFORE UPDATE ON FOOBAR
BEGIN
UPDATE FOOBAR SET record_time = datetime('now', 'localtime')
WHERE rowid = new.rowid;
END
CREATE TRIGGER INSERT_FOOBAR AFTER INSERT ON FOOBAR
BEGIN
UPDATE FOOBAR SET record_time = datetime('now', 'localtime')
WHERE rowid = new.rowid;
END
Test to see if it works...
--INSERT a couple records into the table:
INSERT INTO foobar (RECORD_NO, TO_STORE, UPC, PRICE, EID)
VALUES (0, 1, 'xyz1', 31, '777')
INSERT INTO foobar (RECORD_NO, TO_STORE, UPC, PRICE, EID)
VALUES (1, 1, 'xyz2', 32, '777')
--UPDATE one of the records:
UPDATE foobar SET price = 29 WHERE upc = 'xyz2'
--Check the results:
SELECT * FROM foobar
Hope that helps.
SELECT datetime(CURRENT_TIMESTAMP, 'localtime')
SELECT datetime('now', 'localtime');
Time ( 'now', 'localtime' ) and Date ( 'now', 'localtime' ) works.
You can also just convert the time column to a timestamp by using strftime():
SELECT strftime('%s', timestamp) as timestamp FROM ... ;
Gives you:
1454521888
'timestamp' table column can be a text field even, using the current_timestamp as DEFAULT.
Without strftime:
SELECT timestamp FROM ... ;
Gives you:
2016-02-03 17:51:28
I think this might help.
SELECT datetime(strftime('%s','now'), 'unixepoch', 'localtime');
The current time, in your machine's timezone:
select time(time(), 'localtime');
As per http://www.sqlite.org/lang_datefunc.html