From https://learn.microsoft.com/en-us/sql/t-sql/functions/datepart-transact-sql
The following table lists all datepart arguments with corresponding return values for the statement SELECT DATEPART(datepart,'2007-10-30 12:15:32.1234567 +05:10'). The data type of the date argument is datetimeoffset(7). The nanoseconddatepart return value has a scale of 9 (.123456700) and the last two positions are always 00.
datepart Return value
year, yyyy, yy 2007
quarter, qq, q 4
month, mm, m 10
I wonder what differences are
between year, yyyy, and yy?
between quarter, qq, and q?
between month, mm, and m?
Thanks.
In some cases, the datepart() argument is an English word. The word is unambiguous and clear, both to the person who writes the code and to anyone else who reads it.
In some cases, the datepart() argument is a cryptic collection of one or more letters that bears some relationship to the date part being requested -- however, the relationship is often ambiguous.
Although for a given part, they do the same thing, you can decide which is better to use.
Related
To put a long story short, I am working on a database using PostgreSQL that is managing yelp checkins. The checkintable has the attributes business_id(string), date(string in form yyyy-mm-dd), and time(string in form 00:00:00).
What I simply need to do is, given a business_id, I need to return a list of the total number of checkins based on just the mm (month) value.
So for instance, I need to retrieve the total checkins that were in Jan, Feb, March, April, etc, not based upon the year.
Any help is greatly appreciated. I've already considered group by clauses but I didn't know how to factor in '%mm%'.
Reiterating Gordon, class or not, storing dates and times as strings makes things harder, slower, and more likely to break. It's harder to take advantage of Postgres's powerful date math functions. Storing dates and times separately makes things even harder; you have to concatenate them together to get the full timestamp which means it will not be indexed. Determining the time between two events becomes unnecessarily difficult.
It should be a single timestamp column. Hopefully your class will introduce that shortly.
What I simply need to do is, given a business_id, I need to return a list of the total number of checkins based on just the mm (month) value.
This is deceptively straightforward. Cast your strings to dates, fortunately they're in ISO 8601 format so no reformatting is required. Then use extract to extract just the month part.
select
extract('month' from checkin_date::date) as month,
count(*)
from yelp_checkins
where business_id = ?
group by month
order by month
But there's a catch. What if there are no checkins for a business on a given month? We'll get no entry for that month. This is a pretty common problem.
If we want a row for every month, we need to generate a table with our desired months with generate_series, then left join with our checkin table. A left join ensures all the months (the "left" table) will be there even if there is no corresponding month in the join table (the "right" table).
select
months.month,
count(business_id)
from generate_series(1,12) as months(month)
left join yelp_checkins
on months.month = extract('month' from checkin_date::date)
and business_id = ?
group by months.month
order by months.month
Now that we have a table of months, we can group by that. We can't use a where business_id = ? clause or that will filter out empty months after the left join has happened. Instead we must put that as part of the left join.
Try it.
Why would you store the date as a string? That is a broken data model. You should fix the data.
That said, I recommend converting a date and truncating to the first day of the month:
select date_trunc('day', datestr::date) as yyyymm, count(*)
from t
group by yyyymm
order by yyyymm;
If you don't want these based on the year, then use extract():
select extract(month from datestr::date) as mm, count(*)
from t
group by mm
order by mm;
I have question about function datediff in firebird. When I try to diff two dates like 15.12.1999 and 30.06.2000 in sql like this
SELECT
SUM(datediff (YEAR, W.FROM, W.TO)),
SUM(datediff (MONTH, W.FROM, W.TO)),
SUM(datediff (DAY, W.FROM, W.TO))
FROM WORKERS W
WHEN W.ID=1
I get in result 1 year, 6 month and 198 days but it is not true with value years (of course result should be 0) How I have to write my query to get correct result in parameter year? In that link https://firebirdsql.org/refdocs/langrefupd21-intfunc-datediff.html in documentation there is information about this case but there is not how to solve this problem.
The documentation is not very clear, but I'm pretty sure that datediff() is counting the number of boundaries between two dates. (This is how the very similar function in SQL Server works.) Hence, for year, it is counting the number of "Dec 31st/Jan 1st" boundaries. This is explicitly explained in the documentation.
If you want a more accurate count, you can use a smaller increment. The following is pretty close:
(datediff(day, w.from, t.to) / 365.25) as years_diff
I was reading through a couple of older posts and tried to apply the same logic to my question, I need to extract 13 months of data broken down per month, I would also like to apply the data to relevant headers... any suggestions. Please see code below and error received.
SELECT ST.TXDATE, ST.CODE, ST.QUANTITY
FROM StocTran ST
WHERE ST.TXDATE >= DATEADD(MONTH, -13, CAST(GETDATE() AS DATE))
ORDER BY ST.TXDATE
ERROR: [Elevate Software][DBISAM] DBISAM Engine Error # 11949 SQL
parsing error - Expected end of statement but instead found ( in
SELECT SQL statement at line 3, column 27 Error Code: 11949
DATEADD is a function in MS's TransactSQL for Sql Server. I do not know that DBIsam supports it, and it is not listed in DBIsam's list of supported functions here:
https://www.elevatesoft.com/manual?action=viewtopic&id=dbisam4&product=delphi&version=7&topic=functions
Generally, date functions are not portable across different SQL engines, and from that list, one possibility might be to use the EXTRACT function instead:
The EXTRACT function returns a specific value from a date, time, or timestamp value. The syntax is as follows:
EXTRACT(extract_value
FROM column_reference or expression)
EXTRACT(extract_value,
column_reference or expression)
Use EXTRACT to return the year, month, week, day of week, day, hours, minutes, seconds, or milliseconds from a date, time, or timestamp column. EXTRACT returns the value for the specified element as an integer.
The extract_value parameter may contain any one of the specifiers:
YEAR
MONTH
WEEK
DAYOFWEEK
DAYOFYEAR
DAY
HOUR
MINUTE
SECOND
MSECOND
Even if you are in a hurry, I strngly recommend that you study that page carefully.
UPDATE: From googling dbisam dateadd it looks like Elevate don't have a good answer for an equivalent to DATEADD. One of the hits is this thread:
https://www.sqlservercentral.com/Forums/Topic173627-169-1.aspx
which suggested an alternative way to do it using Delphi's built-in date functions (like IncMonth which I suggested you use in an answer to another q. Basically, you would calculate the start- and end-dates of a range of dates, then convert them to strings to construct a WHERE clause with a column date (from your db) which is equal to or greater than the start date and less or equal to the end date.
I am trying to copy data from one table to another table, which works fine, but I only want to copy certain data from one the of the columns.
Insert Into Period (Invoice_No, Period_Date)
Select Invoice_Seq_No, Inv_Comment
From Invoices
Where INV_Comment LIKE '%November 2015';
The Inv_Comment column contains free-form comments and the date in different formats, e.g. "paid on November 2015 or "paid on Aug" or "July 2015". What I am trying to do is to copy only the "November 2015" part of the comment into the new table.
The above code only copies the entire data of the Inv_Comment field and I only want to copy the date. The date part can be in one of three formats: MON YYYY, DD.MM.YYYY or only the month i.e. MON
How can I extract only the date part I am interested in?
For your very simple example query you can use the substr() function, using the length of your fixed value to count back from the end of the string, as that document describes:
If position is negative, then Oracle counts backward from the end of char.
So you can do:
select invoice_seq_no, substr(inv_comment, -length('November 2015'))
from invoices
where inv_comment like '%November 2015';
But it's clear from the comments that you really want to find all dates, in various formats, and not always at the end of the free-form text. One option is to search the text repeatedly for all the possible formats and values, starting with the most specific (e.g. DD.MM.YYYY) and then going down to least specific
(e.g. just MON). You could insert just the sequence numbers into your table start with, and then repeatedly update the rows that do not yet have values set:
insert into period (invoice_no) select invoice_seq_no from invoices;
update period p
set period_date = (
select case when instr(i.inv_comment, '15.09.2015') > 0 then
substr(i.inv_comment, instr(i.inv_comment, '15.09.2015'), length('15.09.2015'))
end
from invoices i
where i.invoice_seq_no = p.invoice_no
)
where period_date is null;
then repeat the update with another date, or a more generic November 2015 pattern, etc. But specifying every possible date isn't going to be feasible, so you could regular expressions. There are probably better patterns for this but as an example:
update period p
set period_date = (
select regexp_substr(i.inv_comment, '[[0-3][0-9][-./][0-1][0-9][-./][12]?[901]?[0-9]{2}')
from invoices i
where i.invoice_seq_no = p.invoice_no
)
where period_date is null;
which matches (or attempts to match) anything looking like DD.MM.YYYY, followed by maybe:
update period p
set period_date = (
select regexp_substr(i.inv_comment,
'(Jan(uary)?|Feb(ruary)?|Mar(ch)?|Apr(il)?|May|Jun(e)?|Jul(y)?|Aug(ust)?|'
|| 'Sep(tember)?|Oct(ober)?|Nov(ember)?|Dec(ember)?)([[:space:]]+[12]?[901]?[0-9]{2})?')
from invoices i
where i.invoice_seq_no = p.invoice_no
)
where period_date is null;
which matches any short or long month name. You may have mixed case though - aug, Aug, AUG - so you might want to use the match parameter to make it case-insensitive. This isn't supposed to be a complete solution though, and you may need further formats. There are some ideas on other questions.
You may really want actual dates, which means breaking down a bit more, and then assuming missing years - perhaps taking the year from another column (order date?) if it isn't available in the comments, though that gets a bit messy around year-end. But you can essentially do the same thing, just passing each extracted value through to_date() with a format mask matching the search expression you're using.
There will always be mistakes, typos, odd formatting etc., so even if this approach identified most patterns, you'll probably end up with some that are left blank, and will need to be set manually by a human looking at the comments; and some that are just wrong. But this is why dates shouldn't be stored as strings at all - having them mixed in with other text is just making things even worse.
Here you're dealing with strings containing disparate date information. Several string operations may be needed.
I am trying to add months to an existing date in SQL. The new column displayed will have a followup column instead of a days column. Im getting an error in the select statement.can u help?
Create table auctions(
item varchar2(50),
datebought date,
datesold date,
days number
);
Insert into auctions values (‘Radio’,’12-MAY-2001’,’21-MAY-2001’,9);
Select item,datebought,datesold,ADD MONTHS(datesold,3)”followup” from auctions;
Your usage of the add_months() function is incorrect. It's not two words, it's just one (with an underscore)
add_months(datesold, 1)
note the underscore _ between ADD and MONTHS. It's function call not an operator.
Alternatively you could use:
datesold + INTERVAL '1' month
Although it's worth noting that the arithmetics with intervals is limited (if not broken) because it simply "increments" the month value of the date value. That can lead to invalid dates (e.g. from January to February). Although this is documented behaviour (see below links) I consider this a bug (the SQL standard requires those operations to "Arithmetic obey the natural rules associated with dates and times and yield valid datetime or interval results according to the Gregorian calendar")
See the manual for details:
http://docs.oracle.com/cd/E11882_01/server.112/e26088/functions011.htm#i76717
http://docs.oracle.com/cd/E11882_01/server.112/e26088/sql_elements001.htm#i48042
Another thing:
I am trying to add months to an existing date in SQL.
Then why are you using an INSERT statement? To change the data of existing rows you should use UPDATE. So it seems what you are really after is something like this:
update auctions
set datesold = add_months(datesold, 1)
where item = 'Radio';
Your SQL has typographical quotation marks, not standard ones. E.g. ’ is not the same as '. Instead of delimiting a string value, those quotes become part of the value, at least for the particular SQL I have here to test with.
If this doesn't fix your problem, try posting the error you're getting in your question. Magical debugging isn't possible.
This can be used to add months to a date in SQL:
select DATEADD(mm,1,getdate())
This might be a useful link.