I was wondering which of the following is the preferred way to use datediff for datetime types.
datediff(current_date, <datetime type>)
datediff(current_date, date(<datetime type>))
datediff(now(), <datetime type>)
I tried them out on a few cases and they all returned the same answer but I'm worried that they may produce some error down the line.
Is datediff the correct way to find the number of days between two datetime types?
Given:
datediff internally casts parameters to date
now() cast to a date is the same as current_date
There should be no difference in the result between any of those combinations
For your purposes, they are all equivalent.
current_date returns a DATE type, while now() returns DATETIME
This doesn't matter in this case, though, because datediff() ignores the time part of a DATETIME, so using DATE and DATETIME with datediff() are completely equivalent.
Related
How to find the day difference between today's date and a specified date in SQL. The specified date column(P.SubscrpEndDate__c) is in Date time format(12/1/2014 12:00 Am). I have used the below query but it do not works
DATEDIFF(day,GETDATE(), P.SubscrpEndDate__c) AS 'SubscriptionDueDate'
In MySQL, DATEDIFF function, takes only two arguments: end date and start date:
DATEDIFF(NOW(), P.SubscrpEndDate__c) AS 'SubscriptionDueDate'
According to the manual:
DATEDIFF(expr1, expr2) returns expr1 − expr2 expressed as a value in days from
one date to the other.
Also, to get the current date and time you have to use NOW() instead of GETDATE.
It should work in SQL Server. I assume date column(SubscrpEndDate__c) in your table would contain lower values than current date, so simply you can use query below. I've just swapped second & third parameters to get positive difference in days. You can also use ABS() function to ignore negative difference.
SELECT DATEDIFF(day,P.SubscrpEndDate__c,GETDATE() ) AS 'SubscriptionDueDate'
This would work, kindly check
SELECT DATEDIFF(NOW(),P.SubscrpEndDate__c) AS SubscriptionDueDate FROM xyz_table WHERE id='123456'
Does MySQL provide any function which verifies the validity of a date? The DATE function returns NULL upon provision of the invalid date 2013-02-30 for example. However, I am also using STR_TO_DATE simultaneously, which mysteriously stops DATE from working correctly.
SELECT DATE('2013-02-30'); NULL
SELECT STR_TO_DATE('2013-02-30', '%Y-%m-%d'); NOT NULL
SELECT DATE('2013-02-40'); NULL
SELECT STR_TO_DATE('2013-02-40', '%Y-%m-%d'); NULL
SELECT DATE(STR_TO_DATE('2013-02-30', '%Y-%m-%d')); NOT NULL
Why does STR_TO_DATE halt DATE's functionality and is there some workaround to verify if a date is valid when using STR_TO_DATE (which I am obligated to use)?
I have stumbled upon the answer in the meantime: apparently the DATE function skips a few validation checks, when the data type is already that of 'date' (STR_TO_DATE converts strings to date data types). Therefore, converting the date to a string after having parsed it to the correct format with STR_TO_DATE, does the trick:
#valid_date = NOT ISNULL(DATE(CONVERT(STR_TO_DATE('2013-02-29', '%Y-%m-%d'), CHAR))).
It is very difficult to verify if a field is a date because of all the different possible date formats that would need to be taken into account. BUT if you know that the field date formats are one of these:
'yyyy-mm-dd'
'yyyy-mm-dd hh:mm:ss'
'yyyy-mm-dd whatever'
This code will help you:
SELECT count(*) FROM `table`
WHERE DATE(STR_TO_DATE(`column`, '%Y-%m-%d')) IS NOT NULL
AND `column` NOT REGEXP '^[0-9\.]+$'
Basically :
the first condition tells you if is a date, but unfortunately doesn't exclude numbers (ex: DATE(STR_TO_DATE(**1**, '%Y-%m-%d')) = '2001-00-00'
the second ensures that numbers are excluded, which leaves you with dates only that follow the formats above.
If count(*) is >0 then it's a date, if it is 0 it's something else.
Note
This method works for strings of any date format as long as you know in advance what format they follow (which I know is not always the case but still helpful). Just replace the format a priori in STR_TO_DATE
i can't understand your purpose clearly, maybe this is a idea;
SELECT DATE_FORMAT(yourFiled, '%Y-%m-%d') days FROM yourTable GROUP BY days;
this is not null; you can change it. some like
SELECT DATE_FORMAT(yourFiled, '%Y-%m-%d') days FROM yourTable WHERE yourFiled > '2013-9-23 00:00:00' GROUP By days;
Try this:
SELECT DATE(STR_TO_DATE('2013-00-30', '%Y-%m-%d')); --is also NOT NULL
The old DATEDIFF() allowed users to use 3 parameters, and I was trying to do this so I could get hours out of my DATEDIFF rather than days, (I'm trying to show hours since a post). In my database I'm using a TIMESTAMP and this line of code to pull a value, and obviously it doesn't work because I have the extra parameter. Once I remove the 'hour' or 'hh' the query runs and returns a value in days.
SELECT DATEDIFF(hour, CURDATE(), (SELECT Post_Date FROM Post_T WHERE pk_PostID = 1) )
Is there an easy way I can return the hourly value?
Also I'm using MYSQL Version 5.5.20.
Like it says in the documentation:
DATEDIFF(expr1,expr2)
DATEDIFF() returns expr1 – expr2 expressed as a value in days from one
date to the other. expr1 and expr2 are date or date-and-time
expressions. Only the date parts of the values are used in the
calculation.
If you want the result in hours you should use Timestampdiff
TIMESTAMPDIFF(unit,datetime_expr1,datetime_expr2)
Returns datetime_expr2 – datetime_expr1, where datetime_expr1 and
datetime_expr2 are date or datetime expressions. One expression may be
a date and the other a datetime; a date value is treated as a datetime
having the time part '00:00:00' where necessary. The unit for the
result (an integer) is given by the unit argument.
The unit argument can be: MICROSECOND (microseconds), SECOND, MINUTE, HOUR, DAY, WEEK, MONTH, QUARTER, or YEAR.
In your case you can do:
SELECT TIMESTAMPDIFF(hour, CURDATE(), (SELECT Post_Date FROM Post_T WHERE pk_PostID = 1) )
select DATE_FORMAT('8:48:30 AM', '%H:%i:%s')
It returns Null why ?
but when using
select DATE_FORMAT(CURTIME(), '%H:%i:%s')
It return formatted value.
It's returning NULL because MySQL isn't successfully parsing the string into a valid DATETIME value.
To fix the problem, use the STR_TO_DATE function to parse the string into a TIME value,
SELECT STR_TO_DATE('8:48:30 AM', '%h:%i:%s %p')
Then, to get the TIME value converted to a string in a particular format, use the TIME_FORMAT function, e.g. 24-hour clock representation:
SELECT TIME_FORMAT(STR_TO_DATE( '8:48:30 AM', '%h:%i:%s %p'),'%H:%i:%s')
returns:
--------
08:48:30
The method DATE_FORMAT is used to display date and time, however in the first you are not assigning any date except time, so its is throwing null.
From the manuals -
DATE_FORMAT Formats the date value according to the format string.
In MySql version 5.5 SELECT DATE_FORMAT( CURTIME( ) , '%H:%i:%s' ) returns null
DATE_FORMAT 's first parameter is of type DATETIME. On recent mysql server versions both your queries return NULL.
So the answer to your question is that this difference in behaviour is because of a bug in your mysql version - in some way it converts the TIME to DATETIME, while it cannot convert the string to DATETIME.
Here is also an example of a working query:
select DATE_FORMAT(NOW(), '%H:%i:%s')
NOW() returns a DATETIME while CURTIME() returns TIME.
To my knowledge, I think it's because MySQL recognises the function as a time, and therefore knows how to handle it. Whereas, in the first example, it regards it as a string and doesn't know what to do with it.
I wasn't able to find out (googling, reading mysql reference manual) how to get value of DATETIME in seconds in MySQL.
I dont mean to extract seconds from datetime, but to convert it into seconds.
If by "convert to seconds", you mean "convert to an UNIX Timestamp" (i.e. number of seconds since 1970-01-01), then you can use the UNIX_TIMESTAMP function :
select UNIX_TIMESTAMP(your_datetime_field)
from your_table
where ...
And, for the sake of completness, to convert from an Unix Timestamp to a datetime, you can use the FROM_UNIXTIME function.
If you want to have the difference between two DATETIME values, use TIMESTAMPDIFF:
TIMESTAMPDIFF(unit,datetime_expr1,datetime_expr2)
Returns datetime_expr2 – datetime_expr1, where datetime_expr1 and datetime_expr2 are date or datetime expressions. One expression may be a date and the other a datetime; a date value is treated as a datetime having the time part '00:00:00' where necessary. The unit for the result (an integer) is given by the unit argument. The legal values for unit are the same as those listed in the description of the TIMESTAMPADD() function.
mysql> SELECT TIMESTAMPDIFF(MONTH,'2003-02-01','2003-05-01');
-> 3
mysql> SELECT TIMESTAMPDIFF(YEAR,'2002-05-01','2001-01-01');
-> -1
mysql> SELECT TIMESTAMPDIFF(MINUTE,'2003-02-01','2003-05-01 12:05:55');
-> 128885
unit can also be HOUR which is what you asked for in one of the comments.
The unit argument can be any of the following:
MICROSECOND
SECOND
MINUTE
HOUR
DAY
WEEK
MONTH
QUARTER
YEAR
The level of usefulness of some of the other options will of course be determined by the granularity of the data. For instance, "MICROSECOND" will only have limited use if you are not storing microseconds in your DATETIME values.
Use TIME_TO_SEC in previous versions for mysql
SELECT TIME_TO_SEC(time column) FROM table
i used in mysql
TO_SECONDS(your date goes here) method to convert date to seconds from year 0
http://dev.mysql.com/doc/refman/5.5/en/date-and-time-functions.html
The function UNIX_TIMESTAMP(datetime) returns the unix time, which happens to be the number of seconds since 1-Jan-1970 0000 UTC. That may be what you need, but not if you're dealing with dates of birth, historical dates, or dates after 2037.
Starting in mysql 5.5.0 you can use to_seconds()
TO_SECONDS(FIELD_NAME)
FIELD_NAME must be DATETIME type
I have created my own query for your problem:
SELECT HOUR(`colname`) * 3600 + MINUTE(`colname`) * 60 + SECOND(`colname`)
FROM widgets
WHERE id = 1;
Use id = 1 if you have to take a specific row.
The output will be in seconds.