Will It Bit?

Louis Davidson wants to see what he can cast to a bit type:

There are no other textual/alpha string values that will cast to a bit value, but the numeric values that will cast to a bit are voluminous (even some that are in string format). Consider the following eight statements:

SELECT CAST(100 AS bit);
SELECT CAST(-100 AS bit);
SELECT CAST(99999999999999999999999999999999999999 AS bit);
SELECT CAST(-99999999999999999999999999999999999999 AS bit);
SELECT CAST(88.999999 AS bit);
SELECT CAST('1' AS bit);
SELECT CAST('2' AS bit);
SELECT CAST('999999' AS bit);

Danged if they didn’t all work, and all return 1.

Check out what else Louis tries to cast to a bit type.

Using DATETIMEOFFSET

Randolph West continues his date and time data type series:

DATETIMEOFFSET works the same way as the DATETIME2 data type, except that it is also time zone aware. It is formatted as 'YYYY-MM-DD HH:mm:ss[.nnnnnnn][{+|-}hh:mm]'.

Got all that? YYYY represents a four-digit year, MM is a two-digit month between 1 and 12, DD is a two-digit day between 1 and 31 depending on the month, HH represents a two-digit hour between 0 and 23, mm is the minutes between 0 and 59, while ss is the number of seconds between 0 and 59. Once again, n represents between zero and seven decimal places in a fraction of a second.

The main difference from DATETIME2 is the time zone offset at the end, which is the number of hours and minutes as an offset from UTC time.

Read on for more.  I generally don’t use this date type much, preferring to stick with DATETIME2 and saving data as UTC.

DATETIME2 In SQL Server

Randolph West continues his SQL Server date & time data types series:

SQL Server 2008 introduced new data types to handle dates and times in a more intelligent way than the DATETIME and SMALLDATETIME types that we looked at previously.

This week, we look at the DATETIME2 data type. I’m not the first person to think that this was probably not the best name for a data type, but here we are, a decade later.

DATETIME2 is, at its heart, a combination of the DATE and TIME data types we covered in previous weeks. DATE is 3 bytes long and TIME is between 3 and 5 bytes long depending on accuracy. This of course means that DATETIME2 can be anything from 6 to 8 bytes in length.

Nowadays, if you want to store a date plus time, this should be your default, not DATETIME.

The TIME Data Type

Randolph West covers the TIME data type in SQL Server:

This week, we look at the TIME data type. It is formatted as HH:mm:ss.fffffff, where HH is hours between 0 and 23, mmis minutes between 0 and 59, ss is seconds between 0 and 59, and f represents 0 or more fractional seconds, up to a maximum of seven decimal places.

With a maximum length of 5 bytes, TIME can store a value with a granularity of up to 100 nanoseconds.

I tend not to use TIME very often.  It’s useful if you need it, but I rarely find myself needing a dateless time.

The Date Data Type

Randolph West continues his dates and times series:

QL Server 2008 introduced new data types to handle dates and times in a more intelligent way than the previous DATETIME and SMALLDATETIME types that we looked at previously.

The first one we look at this week is DATE. Whereas DATETIME uses eight bytes and SMALLDATETIME uses four bytes  to store their values, DATE only needs a slender three bytes to store any date value between 0001-01-01 and 9999-12-31inclusive.

The DATE data type was a fantastic addition to SQL Server 2008.

Don’t Use SMALLDATETIME

Randolph West argues against using the SMALLDATETIME data type:

But let’s say you don’t need that kind of accuracy and are happy with a granularity to the nearest minute. Maybe you’re storing time cards and don’t think it’s necessary to store seconds. As discussed in the Fundamentals series, you really want to choose the most appropriate datatype for your data.

Enter SMALLDATETIME, which rounds up or down to the nearest minute. The seconds value for any SMALLDATETIME is 00. Values of 29.999 seconds or higher are automatically rounded up to the nearest minute, while values of 29.998 seconds or lower are rounded down.

Read on to see Randolph’s explanation of why he recommends against using SMALLDATETIME.

The DATETIME Type In SQL Server

Randolph West gets into the DATETIME data type:

DATETIME is an eight-byte datatype which stores both a date and time in one column, with an accuracy of three milliseconds. As we’ll see though, the distribution of this granularity may not be exactly what we’d expect.

Valid DATETIME values are January 1, 1753 00:00:00.000, through December 31, 9999 23:59:59.997. On older databases designed prior to SQL Server 2008, because there was no explicit support for date values, it was sometimes customary to leave off the time portion of a DATETIME value, and have it default to midnight on that morning. So for example today would be stored as February 21, 2018 00:00:00.000.

If you’re not particularly familiar with SQL Server data types, this is detailed enough information to get you going and to explain exactly why you shouldn’t use DATETIME anymore…

Converting Int To Time

Bill Fellows has a pop quiz for us:

Given the following DDL

CREATE TABLE dbo.IntToTime
( CREATE_TIME int
);

What will be the result of issuing the following command?

ALTER TABLE dbo.IntToTime ALTER COLUMN CREATE_TIME time NULL;

Clearly, if I’m asking, it’s not what you might expect.

Click through if you have not memorized your implicit conversion tables.

Using Date Types In Warehouses

Koen Verbeeck argues that date keys in warehouses should be actual date types:

The worst are by far the string representation, as there is no actual check on the contents. It can literally contain everything. And is ’01/02/2018′ the first of February 2018 (like any sane person would read, because days come before months), or the 2nd of January? So if you have to store dates in your data warehouse, avoid strings at all costs. No excuses.

The integer representation – e.g. 20171208 – is really popular. If I recall Kimball correctly, he said it’s the one exception where you can use smart keys, aka surrogate keys that have a meaning embedded into them. I used them for quite some time, but I believe I have found a better alternative: using the actual date data type.

I bounce back and forth, but I’m sympathetic to Koen’s argument, which you can read by clicking through.

Appropriate Data Types And Unicode

Raul Gonzalez on (in)appropriate use of National character strings:

Yes, you have read it… I see dates stored as NVARCHAR(10) and NCHAR(10) on daily basis, please don’t ask me why.

This case is even worse, because DATE takes 3 bytes where NCHAR(10) takes 20 bytes, yes Ladies and Gentlemen more than 6 times more space to store the same data.

But wait! how can you be certain that those ten characters are actually a valid date? You can’t, unless you reinvent the wheel and validate that those dates are obviously valid dates and pay the performance penalty of doing it.

You’d think that picking the right data type for something would be fairly easy and then you find a table with a few dozen NVARCHAR(MAX) columns.

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