Simple question. I have tried searching on Google and after about 6 searches, I figured it would be faster here.
How big is an int in SQL?
-- table creation statement.
intcolumn INT(N) NOT NULL,
-- more table creation statement.
How big is that INT(N) element? What's its range? Is it 2^N or is it N Bytes long? (2 ^ 8N)? Or even something else I have no idea about?
It depends on the database. MySQL has an extension where INT(N) means an INT with a display width of 4 decimal digits. This information is maintained in the metadata.
The INT itself is still 4 bytes, and values 10000 and greater can be stored (and probably displayed, but this depends how the application uses the result set).
Related
In working on a project, where:
A dataset is collected every 10 seconds, which is stored in an SQlite file on an server.
After being processed, the data is sent to an SQL-Database every 5 minutes.
Afterwards the data in the SQlite file, which isn't needed anymore, gets deleted.
The collecting of the data continues and at the moment the id doens't get reset.
I didn't get how much an integer in SQLite can store according to the documentation (https://www.sqlite.org/datatype3.html).
In MySQL-Databases the maximum value of an interger column is 2.147.483.647. If my script would run for 10 years the id would be 31.449.600. Although this would be much lower less than the maximum, I wondered,
if there is any problem with storing high values in SQlite.
Could this affect the performance?
That page mentions that integer numbers can be stored in up to 8 bytes, i.e., 64 bits.
As mentioned elsewhere, this means that the largest allowed integer is 9,223,372,036,854,775,807.
An integer in SQLite can store values up to 9223372036854775807 (8 Bytes signed so 63 bits as 1 bit is for the sign), which is the same as a MySQL BIGINT (which is in addition to the Standard INT).
Should I define a column type from actual length to nth power of 2?
The first case, I have a table column store no more than 7 charactors,
will I use NVARCHAR(8)? since there maybe implicit convert inside Sql
server, allocate 8 space and truncate automatic(heard some where).
If not, NCHAR(7)/NCHAR(8), which should be(assume the fixed length is 7)
Any performance differ on about this 2 cases?
You should use the actual length of the string. Now, if you know that the value will always be exactly 7 characters, then use CHAR(7) rather than VARCHAR(7).
The reason you see powers-of-2 is for columns that have an indeterminate length -- a name or description that may not be fixed. In most databases, you need to put in some maximum length for the varchar(). For historical reasons, powers-of-2 get used for such things, because of the binary nature of the underlying CPUs.
Although I almost always use powers-of-2 in these situations, I can think of no real performance differences. There is one. . . in some databases the actual length of a varchar(255) is stored using 1 byte whereas a varchar(256) uses 2 bytes. That is a pretty minor difference -- even when multiplied over millions of rows.
In the table definition I saw:
Latitude -> varchar(50)
Longitude -> nvarchar(50)
Immediately, obviously, I queried the thinking behind this - being positively sure these values are in fact numerical by nature. Long story short: I postulated that these will be numerical, decimal in fact, and we would discard the 'thinking-in-strings' philosophy.
Now for the horns of my dilemma, I just went ahead and typed:
Latitude -> decimal(2, 4)
But hold on a second, 4 ain't right, right? Right. So I thought I'd up the threshold before realising (in a split second might I add) that 6 or 8 might not not cut it either. So, first things first...
Am I right in insisting we even go about it this way? And if so...
To what precision ought these values be stored to ensure we can persist the entire value which is to be inserted? For example, is there anything predefined by specification?
I don't just want to use something like Latitude -> decimal(2, 16) simply for it to be just as flawed as decimal(2, 2) in principle. And a similar question arises for Longitude specifically but I'm assuming the answer to one will suffice for the other, i.e decimal(3, answer).
We are using MSSQL Server 2005.
It seems I am educating myself with SQL Server by manual experience and therefore rendering parts of this question irrelevant: I can only use decimal(x, max(x)) not decimal(x, y) anyway! Will leave the question as is for input.
Decimal(2, 4) means 2 total digits of precision and 4 behind the decimal. SQL Server won't let you do that, but I think it would means you can store values from -0.0099 to 0.0099.
I'd recommend decimal(9, 6). This will store with an accuracy down to about 1/6th of an inch at the equator. Using 9 or less as the precision requires 5 bytes of storage, using 10-19 requires 9 bytes.
The maximum precision of decimals in sql server is currently 38. The scale can be up to 38. At it's max, a decimal will take up 17 bites, where as a varchar takes up whatever the length is plus 2. So if you went with a varchar(38), at it's max you're taking up 40 bits of data. The flip side is that a varchar is not as limited in size as a decimal is. So what you really need to do is figure out how many decimal points you're going to allow and then figure out your data type for it.
Source Info
I have a django app that uses MySQL as the database backend. It's been running for a few days now, and I'm up to ID 5000 in some tables already.
I'm concerned about what will happen when I overflow the datatype.
Is there anyway to tell the auto increment to start over at some point? My data is very volatile, so when I do overflow the ID, there is no possible way that ID 0, or anywhere near that will still be in use.
Depending on whether you're using an unsigned integer or not and which version of MySQL you're running, you run the rink of getting nasty negative values for the primary key or (worse) the row simply won't be inserted and will throw an error.
That said, you can easily change the size/type of the integer in MySQL using an ALTER command to preemptively stop this from happening. The "standard" size for an INT being used as a primary key is an INT(11), but the vast majority of DB applications don't need anything nearly that large. Try a MEDIUMINT.
MEDIUMINT - The signed range is –8388608 to 8388607. The unsigned range is 0 to 16777215
As compared to....
INT or INTEGER - The signed range is –2147483648 to 2147483647. The unsigned range is 0 to 4294967295
There's also the BIGINT, but to be honest you've probably got much larger scalability issues than your data types to worry about if you have a table with > 2 billion rows :)
Well, the default 32bit INT goes up to about 2 billion. At 5000 IDs per day, that's about 1000 years till overflow. I don't think you have to worry yet...
Why would someone use numeric(12, 0) datatype for a simple integer ID column? If you have a reason why this is better than int or bigint I would like to hear it.
We are not doing any math on this column, it is simply an ID used for foreign key linking.
I am compiling a list of programming errors and performance issues about a product, and I want to be sure they didn't do this for some logical reason. If you follow this link:
http://msdn.microsoft.com/en-us/library/ms187746.aspx
... you can see that the numeric(12, 0) uses 9 bytes of storage and being limited to 12 digits, theres a total of 2 trillion numbers if you include negatives. WHY would a person use this when they could use a bigint and get 10 million times as many numbers with one byte less storage. Furthermore, since this is being used as a product ID, the 4 billion numbers of a standard int would have been more than enough.
So before I grab the torches and pitch forks - tell me what they are going to say in their defense?
And no, I'm not making a huge deal out of nothing, there are hundreds of issues like this in the software, and it's all causing a huge performance problem and using too much space in the database. And we paid over a million bucks for this crap... so I take it kinda seriously.
Perhaps they're used to working with Oracle?
All numeric types including ints are normalized to a standard single representation among all platforms.
There are many reasons to use numeric - for example - financial data and other stuffs which need to be accurate to certain decimal places. However for the example you cited above, a simple int would have done.
Perhaps sloppy programmers working who didn't know how to to design a database ?
Before you take things too seriously, what is the data storage requirement for each row or set of rows for this item?
Your observation is correct, but you probably don't want to present it too strongly if you're reducing storage from 5000 bytes to 4090 bytes, for example.
You don't want to blow your credibility by bringing this up and having them point out that any measurable savings are negligible. ("Of course, many of our lesser-experienced staff also make the same mistake.")
Can you fill in these blanks?
with the data type change, we use
____ bytes of disk space instead of ____
____ ms per query instead of ____
____ network bandwidth instead of ____
____ network latency instead of ____
That's the kind of thing which will give you credibility.
How old is this application that you are looking into?
Previous to SQL Server 2000 there was no bigint. Maybe its just something that has made it from release to release for many years without being changed or the database schema was copied from an application that was this old?!?
In your example I can't think of any logical reason why you wouldn't use INT. I know there are probably reasons for other uses of numeric, but not in this instance.
According to: http://doc.ddart.net/mssql/sql70/da-db_1.htm
decimal
Fixed precision and scale numeric data from -10^38 -1 through 10^38 -1.
numeric
A synonym for decimal.
int
Integer (whole number) data from -2^31 (-2,147,483,648) through 2^31 - 1 (2,147,483,647).
It is impossible to know if there is a reason for them using decimal, since we have no code to look at though.
In some databases, using a decimal(10,0) creates a packed field which takes up less space. I know there are many tables around my work that use that. They probably had the same kind of thought here, but you have gone to the documentation and proven that to be incorrect. More than likely, I would say it will boil down to a case of "that's the way we have always done it, because someone one time said it was better".
It is possible they spend a LOT of time in MS Access and see 'Number' often and just figured, its a number, why not use numeric?
Based on your findings, it doesn't sound like they are the optimization experts, and just didn't know. I'm wondering if they used schema generation tools and just relied on them too much.
I wonder how efficient an index on a decimal value (even if 0 scale is set) for a primary key compares to a pure integer value.
Like Mark H. said, other than the indexing factor, this particular scenario likely isn't growing the database THAT much, but if you're looking for ammo, I think you did find some to belittle them with.
In your citation, the decimal shows precision of 1-9 as using 5 bytes. Your column apparently has 12,0 - using 4 bytes of storage - same as integer.
Moreover, INT, datatype can go to a power of 31:
-2^31 (-2,147,483,648) to 2^31-1 (2,147,483,647)
While decimal is much larger to 38:
- 10^38 +1 through 10^38 - 1
So the software creator was actually providing more while using the same amount of storage space.
Now, with the basics out of the way, the software creator actually limited themselves to just 12 numbers or 123,456,789,012 (just an example for place holders not a maximum number). If they used INT they could not scale this column - it would go up to the full 31 digits. Perhaps there is a business reason to limit this column and associated columns to 12 digits.
An INT is an INT, while a DECIMAL is scalar.
Hope this helps.
PS:
The whole number argument is:
A) Whole numbers are 0..infinity
B) Counting (Natural) numbers are 1..infinity
C) Integers are infinity (negative) .. infinity (positive)
D) I would not cite WikiANYTHING for anything. Come on, use a real source! May as well be http://MyPersonalMathCite.com