Category: Dates and Numbers

Daniel Hutmacher has started to create a comprehensive calendar table:

It’s a collection of inline table value functions that generate different types of calendars, with a number of properties that could be relevant for a calendar dimension. Each function has a unique date column, so you can join the functions you need together in a view or a procedure. The functions are:

• Dates: a plain gregorian calendar.

• Fiscal, annual: a gregorian, year-based calendar where you can define the start of a year, like a corporate fiscal calendar.

• Fiscal, 4-4-5 or 52/53: a week-based calendar where years comprise four quarters of 4+4+5 weeks respectively.

• Indian national calendar

• Persian calendar

• Thai calendar

• Dates of Catholic and Orthodox easter

• Lunar cycle

I was going to jokingly be shocked that this list didn’t include the Hebrew or Islamic calendars, but then Daniel had to ruin my fun by explaining why not.  Check it out and when you’re ready to give it a try, head over to his downloads page.

Randolph West continues his dates and times series with a new function, DATENAME():

There are many similarities between DATEPART and DATENAME. Where DATEPART returns the date or time part as an integer, DATENAME returns the part as a character string.

This DATENAME function also takes two parameters: the date or time part we want back, and the input date. Just as we saw with DATEPART, the documentation indicates the input date parameter must be an “expression that can resolve to one of the following data types: date, smalldatetime, datetime, datetime2, datetimeoffset, or time.”

Similarly, the date and time parts that can be returned look much like those in DATEPART, which gives us another opportunity for the reminder that we should avoid using the available abbreviations in order to help with writing clearly understandable code.

DATENAME is a useful function for displaying parts of dates & times, but Randolph does lay out the caveats.

Randolph West shares some thoughts on the DATEPART function:

As we learned some time ago, an INT (integer) in T-SQL uses four bytes, and has a maximum value greater than zero of over 2 billion (there are more than 4 billion values in an integer if we take the negative values into account).

Why then are date and time parts expressed as an INT, which have a lot of overhead for values like 24, 31, and 60?

There are two reasons:

1. Integers make things simpler. When writing arithmetic in T-SQL and other programming languages, the default data type is usually an integer. Having to memorise which data types are returned from built-in functions becomes unnecessary when we know it will be an INT. Yes, it uses extra memory, but four bytes is a reasonable trade-off against complexity.

2. One of the return values is nanoseconds. Although DATETIME2(7) only has a granularity down to 100 nanoseconds, DATEPART allows us to return this value, which requires a data type large enough to contain an integer up to 1 billion (nanoseconds can range from 0 to 999,999,900 in increments of 100).

Randolph also explains what happened a few years back to cause iPhone alarms not to fire on January 1st and 2nd.

Wayne Sheffield compares the performance of four methods for removing time from a DateTime data type:

Today, we’ll compare 3 other methods to the DATEADD/DATEDIFF method:

1. Taking advantage of the fact that a datetime datatype is stored as a float, with the decimal being fractions of a day and the whole numbers being days, we will convert the datetime to float, taking the floor (just the whole numbers), and converting back to datetime.
2. Using the DATEADD/DATEDIFF routine.
3. Converting the datetime to DATE and back to datetime.
4. Converting the datetime to varbinary (which returns just the time), and subtracting that from the datetime value.

While there are other ways of stripping the time (DATETIMEFROMPARTS, string manipulation), those ways are already known as poorly performing. Let’s just concentrate on these four.

Click through for the methods, as well as a performance test to see which is fastest.

Randolph West shows a few functions which can retrieve current date and time information:

What do we mean by local date and time?

As discussed previously, SQL Server is not time zone aware, nor does it have to be. This is because the operating system that SQL Server runs on can have multiple custom regional settings depending on which user is logged into the server.

This holds true for the SQL Server service account as well, which is just another user on the operating system. When any of these functions is called, it is asking for the date and time from the operating system.

If you’re going to use DATETIME2 (which you generally should), take advantage of the precision that SYSUTCDATETIME() gives you over GETUTCDATE().

Claudio Silva points out a difference between the DATETIME and DATETIME2 data types:

I’m currently working on a SQL code migration from Firebird to SQL Server and I hit an error that I haven’t seen for some time.

The error message is the following:

Msg 206, Level 16, State 2, Line 4
Operand type clash: datetime2 is incompatible with int

This ringed the bell right away! Somewhere on the code someone was trying to do an arithmetic calculation without using the proper function.

Read on for the solution.