Lets say I have a table Student with columns Name,DOJ,TOJ.
Inorder to enter date in mm/dd/yyyy format and timestamp in the format hh24:mm:ss I used ALTER SESSION SET NLS_DATE_FORMAT='MM/DD/YYYY' and ALTER NLS_TIMESTAMP_FORMAT='HH24:MI:SS' but i want to know an alternative solution to enter in this format without involving session. Please guide me through this.
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We store dates/times either in a DATE column (which is Oracle's inappropriate name for a datetime) or a TIMESTAMP column (which has more precision and can handle timezones, too). These types have no format. This is important, because thus comparing and sorting them in the database works fine, because the DBMS knows how to handle datetimes, while the users see the date in their format. I, for instance, have set my Windows to German, so I will see the datetimes in some German format, while you will see the same date in a format you are used to.
There are few situations where you want to store date and time separately. The reason is typically that you can set them null. A date without a time means "the whole day". A time without a date means "every day this time". But then you often want this even more advanced anyway ("every Tuesday and Wednesday", "every December 24", etc.) for which you need soemthing more sophisticated then just date and time split into two.
So, usually we just store date and time combined. For a precision down to seconds we use DATE. If we wanted them separately we'd have to think of an appropriate data type, because Oracle has no real date type and no time type either. So we'd either use DATE and ignore the date part or the time part or we use strings. The former solution is usually preferred, because you cannot mistakenly enter invalid data like February 30 or 23:66:00.
If you want to store formatted dates and times, you are talking about strings. I don't recommend this. Strings are not the appropriate data types for dates and times. And a format '01/02/2000' is ambiguous. Some people will read this as February 1, others as January 2.
If you wanted to do this, you would have to change the column types to VARCHAR2 and simply store values like '02/25/2021' and '13:28:56'.
But if you wanted to sort your data or compare dates/times then or just show them to a foreign user in a format they are used to, you would always have to convert them. E.g.:
select *
from mytable
order by to_date(doj || ' ' || toj, 'mm/dd/yyyy hh24:mi:ss');
I am afraid that to change default format you have no other option but to change NLS_DATE_FORMAT either in database level or session level.
But If your purpose is to show the date in a specific format in the front end then you can use to_char() function as below:
SELECT NAME, to_CHAR(DOJ,'dd/mm/yyyy'),to_CHAR(TOJ,'HH24:MI:SS') FROM table
To change the default date format in system level:
ALTER SYSTEM SET NLS_DATE_FORMAT='DD/MM/YYYY' scope=both;
You can also change the default date format at startup time with a login trigger to change the nls_date_format:
CREATE OR REPLACE TRIGGER CHANGE_DATE_FORMAT
AFTER LOGON ON DATABASE
call DBMS_SESSION.SET_NLS('NLS_DATE_FORMAT','YYYYMMDD');
Related
I want to create a column of data type having only 'mm-dd' values.
Is it possible and if yes how should I do it?
Note: Instead of "2022-06-07", I want "07-06"
There is no date type that can store that format - in fact none of the date types store a date and/or time in any of the formats you typically recognize.
For your specific requirement, that looks like a char(5) for the data type, but how you constrain it so that it will only accept valid date values, I have no idea. You'd think this would work:
CHECK (TRY_CONVERT(date, string_column + '-2022', 105) IS NOT NULL)
But what about leap years? February 29th is sometimes valid, but you've thrown away the only information that can make you sure. What a bunch of mess to store your favorite string and trust that people aren't putting garbage in there.
Honestly I would store the date as a date, then you can just have a computed column (or a column in a view, or just do this at query time:
d_slash_m_column AS CONVERT(char(5), date_column, 105)
Why not just in your query (or only in a view) say:
[output] = CONVERT(char(5), data_in_the_right_type, 105)
?
I'd personally stay away from FORMAT(), for reasons I've described here:
FORMAT() is nice and all, but…
FORMAT is a convenient but expensive function - Part 1
FORMAT is a convenient but expensive function - Part 2
You can use the SQL Server FORMAT function:
FORMAT(col1, 'dd/MM')
Check the demo here.
In such cases using char or varchar is not the best option as in those cases the underlying DB constraints that validate the integrity of the data do not kick in.
Best option is to use an arbitrary year and then put in a proper date, so for example for storing 01-Jan, the db column should store proper date with year as any arbitrary value, e.g. 2000. So your db should say 2000-01-01.
With such a solution you are still able to rely on the DB to raise an error if you tried month 13. Similarly sorting will work naturally as well.
I work in T-SQL but have been given some Oracle PL-SQL for review on a Project.
Within the code there are Multiple WHERE clauses that do comparison of a Field of DataType = DATE against Strings which hold a "date".
ex:
WHERE to_date(mytable.mydatefield) > '23-OCT-2015'
OR
WHERE mytable.mydatefield > '23-OCT-2015'
Q1: Since "mydatefield" is already defined as a DATA type, isn't doing a "to_date" unnecessary?
Q2: Will Oracle do an implicit conversion on the '23-OCT-2015' and convert it to a date for comparison? I seem to remember encountering this before and comparing DATES to STRINGS caused issues?
Am I incorrect about that? If not can someone give me an example that I can use as evidence that it would not work?
A1: In general yes, but take the way Oracle handles implicit type conversions into account. The To_Date function around the mydatefield column expects a string input, so Oracle implicitly converts mydatefield to a string with a format matching the NLS_DATE_FORMAT session setting (which defaults to DD-MON-RR). Once converted to a string the To_Date function then converts it back to a date again using the current NLS_DATE_FORMAT setting. The newly reconstituted date is then compared to the string '23-OCT-2015', but since dates and strings aren't directly comparable the string value gets implicitly converted to a date using the current NLS_DATE_FORMAT setting. Depending on the value of the NLS_DATE_FORMAT setting, the first implicit conversion is likely to lose information specifically any time portion AND the original century, since the default NLS_DATE_FORMAT uses only a two digit year RR and no time component.
A2: Possibly, but it's best not to rely on it.
Both relations are poor programming for a couple of reasons. First they both are affected by implicit type conversions from dates to strings (or vice versa). Second they are both attempting to compare dates with strings in a non canonical form. As such 10-DEC-15 is less than 23-OCT-2015 because 1 is less than 2. Also note the difference in the number of digits representing the year since the default NLS_DATE_FORMAT uses a two digit year.
The correct method would be to compare the date column (possibly truncated) to a date string explicitly converted to a date
WHERE mytable.mydatefield > TO_DATE('23-OCT-2015', 'DD-MON-YYYY')
OR with truncation:
WHERE trunc(mytable.mydatefield) > TO_DATE('23-OCT-2015', 'DD-MON-YYYY')
which removes the time component of the date field.
Q1: According to Oracle, the first parameter of to_date() is a char value. Using it like to_date(date_value) you will force an implicit cast of date_value to char and then wrapping it again in a date value.
Q2: The server will do an implicit conversion from the string '23-OCT-2015' to a date value but based on database parameters which can differ from various servers(DEV vs PROD for example) so you should not rely on them. An example of correct usage would be WHERE mytable.mydatefield > to_date('23-OCT-2015','dd-MON-yyyy')
You should always use to_date/to_char to make sure you are using the correct format. Please see this answer for a more detailed explanation: Comparing Dates in Oracle SQL
I need verify that all cells in column contain data in only date format. How it possible to verify?
*I think it isn't LIKE function.
DATE doesn't have any format. What you see is for display purpose so that it could be easily interpreted.
DATE datatype is stored in a proprietary format internally in 7 bytes. It is a bad idea and makes no sense to verify the format while date is stored in an internal format. As I said, format is only for display.
If the date column is not a DATE data type, then it is a design flaw. And, any application based on such a flawed database design is on the verge to break anytime.
Storing DATE values other than date data type is just like not understanding the basics.
You should first fix the design to get a permanent solution. Any solution to your question is just another workaround.
Let me show a small example how it creates even more confusion.
The following date :
01/02/2015
Is it:
1st Feb 2015 or,
2nd Jan 2015
There is no way to tell that. It could be either DD or MM. This being just one among so many other problems due to the incorrect data type.
Store date values as DATE data type only, period.
Based on your last question, I think you are looking for something like this:
SELECT COUNT(*) FROM ...
WHERE NOT REGEXP_LIKE (A, '^XXX/MOSCOW/XXXMSX/[0-9]{4}-[0-9]{2}-[0-9]{2}$')
If count is greater than zero, something doesn't match. If you want more detail on what doesn't match, change your SELECT clause appropriately.
If you are looking for multiple date formats, you can change your regular expression appropriately. The | operator in most flavors of regular expression, including Oracle's, lets you define multiple patterns in the same space. You might use something like
SELECT COUNT(*) FROM ...
WHERE NOT
REGEXP_LIKE (A,
'^XXX/MOSCOW/XXXMSX/[0-9]{4}-[0-9]{2}-[0-9]{2}$|^[0-9]{4}-[0-9]{2}-[0-9]{2}$')
adding as many different matching patterns as you need.
Try
SELECT *
FROM POL
WHERE NOT REGEXP_LIKE(TR_KRY, '^(0[1-9]|([1-2][0-9])|30|31)-(([0][1-9])|10|11|12)-[0-9]{4}$')
This will return you all rows where TR_KRY is not formatted as 'DD-MM-YYYY', where DD is '01'-'31', MM is '01'-'12', and YYYY is any four numeric digits.
As others have said, storing dates as character strings is not a good idea. In the field you're looking at, it might be that the date is stored as DD-MM-YYYY (day-month-year - the usual case in Europe and perhaps elsewhere), or it might be that the date is stored as MM-DD-YYYY (month-day-year - a common practice in the US). If possible, I suggest you should convert this field to the DATE data type so that the TO_CHAR function can be used to produce a text version of the date in whatever format is desired.
Given the example data you've shown in comments (and that's also not good practice - you should go back and edit the question when you want to include additional information) it appears the dates are formatted as DD-MM-YYYY and I've set up the regular expression above to deal with this as best as possible.
I am creating a custom audit log as a process in the Apex application I have developed.
Below is the code I have used to log the actions by the user when they use the application. The LOGON_DT and LOGOFF_DT will only need to be in a date format. However, QUERY_SEARCH_TIME will need the time.
INSERT INTO AUDIT_LOG
(USERNAME, ORDER_NO, ORDER_NAME, CUSTOMER_NAME, LOGON_DT, LOGOFF_DT, QUERY_SEARCH_TIME)
VALUES
(:APP_USER, :P10_ORDER_NO, :P10_ORDER_NAME, :P10_CUSTOMER_NAME, SYSDATE, SYSDATE,
SYSDATE(HH24:MI:SS));
The above code works perfectly when HH24:MI:SS is taken off, and I'm not sure where I'm going wrong with this?
Any guidance will be great. Thank you!
Oracle has it's own internal representation for a DATE datatype. You can't dictate its format in the way you are attempting.
It is common to apply a date format on retrieval, which you can do by applying the appropriate format mask as you convert to a string.
TO_CHAR(QUERY_SEARCH_TIME, 'HH24:MI:SS')
A DATE column already captures a time component. It may not be necessary to cut it off. And if you do, you do not want a DATE column as such a column will always capture a whole date, and what would be the point if you want only time.
To visualize the time component of a date you have to apply a format mask to it:
TO_CHAR(SYSDATE, 'HH24:MI:SS'). If you want to capture just that, the time, then change the datatype of the column to a VARCHAR2 type of sufficient length for the format mask you apply.
Read up on datetime datatypes here: Oracle documentation on datetime types
Read up on datetime format models here: Oracle documentation on format models
If you need time part of date only for output, you can use answer of Tom, but if you really need to store time part only, you can calculate it as
sysdate - trunc(sysdate)
I am designing a database for use with a Ruby on Rails application. For a given object, I need to access the date of an event in both the Gregorian format and the Hebrew calendar equivalent. I can easily convert between the two formats, but the issue is that in the Hebrew calendar, the date changes at sunset, not midnight. Therefore, I'll need to either store two separate dates, or store a Gregorian date and a separate boolean field, after_sunset. Then, whenever I need to access the Hebrew date, I'll need to query for both fields, convert the date, and if after_sunset==true, increment the date.
Which of these options is considered "better"?
And, if I store the Hebrew date separately, is it best to store it as a String, an Integer, or can I use a regular Date?
With an after_sunset flag you store a Gregorian date and add all the additional information needed to know the Hebrew date.
With two dates you would store the two dates explicitely. However, to have data consistent you would install a check constraint to ensure that the dates match. This is because the two dates share part of their information (redundancy). This means the data is not normalized.
For this reason, to have data normalized in your database (and thus not having to install a check constraint to keep the data consistent) the first approach is better. Store the date plus an after- sunset flag.
Store the date in UTC and also store in unix format
You can use conversion function based on the type
This will allow your database to support other date time formats easily in the future
Unless you are going back to the dawn of time, I think I would simply have a many-year lookup table of UTC datetimes and Hebrew dates where the UTC column is the first second of the Hebrew day in a specific time zone (Greenwich?).
Conversions are a quick binary search,
SELECT hebrew_date FROM hebrew_gregorian_lookup
WHERE some_input_time >= gregorian_cutoff
ORDER BY gregorian_cutoff DESC LIMIT 1;
If you index and cluster the lookup table on gregorian_cutoff, it should be very quick, even for 100 years. (If your RDBMS has a way to force a table into RAM, even better.) Also depending on your RDBMS, you may be able to wrap this in a function/procedure with no loss of efficiency.
I suggest storing the Hebrew date not as a string but as a record of three shorts, day, month, year. You can have a tiny lookup table for month to string, or perhaps use an enumeration. That will give you some flexibility in formatting, e.g., Hebrew characters vs. Latin in the output.