I am using character varying data type in PostgreSQL.
I was not able to find this information in PostgreSQL manual.
What is max limit of characters in character varying data type?
Referring to the documentation, there is no explicit limit given for the varchar(n) type definition. But:
...
In any case, the longest possible
character string that can be stored is
about 1 GB. (The maximum value that
will be allowed for n in the data type
declaration is less than that. It
wouldn't be very useful to change this
because with multibyte character
encodings the number of characters and
bytes can be quite different anyway.
If you desire to store long strings
with no specific upper limit, use text
or character varying without a length
specifier, rather than making up an
arbitrary length limit.)
Also note this:
Tip: There is no performance
difference among these three types,
apart from increased storage space
when using the blank-padded type, and
a few extra CPU cycles to check the
length when storing into a
length-constrained column. While
character(n) has performance
advantages in some other database
systems, there is no such advantage in
PostgreSQL; in fact character(n) is
usually the slowest of the three
because of its additional storage
costs. In most situations text or
character varying should be used
instead.
From documentation:
In any case, the longest possible character string that can be stored is about 1 GB.
character type in postgresql
character varying(n), varchar(n) = variable-length with limit
character(n), char(n) = fixed-length, blank padded
text = variable unlimited length
based on your problem I suggest you to use type text. the type does not require character length.
In addition, PostgreSQL provides the text type, which stores strings of any length. Although the type text is not in the SQL standard, several other SQL database management systems have it as well.
source : https://www.postgresql.org/docs/9.6/static/datatype-character.html
The maximum string size is about 1 GB. Per the postgres docs:
Very long values are also stored in background tables so that they do not interfere with rapid access to shorter column values. In any case, the longest possible character string that can be stored is about 1 GB. (The maximum value that will be allowed for n in the data type declaration is less than that.)
Note that the max n you can specify for varchar is less than the max storage size. While this limit may vary, a quick check reveals that the limit on postgres 11.2 is 10 MB:
psql (11.2)
=> create table varchar_test (name varchar(1073741824));
ERROR: length for type varchar cannot exceed 10485760
Practically speaking, when you do not have a well rationalized length limit, it's suggested that you simply use varchar without specifying one. Per the official docs,
If you desire to store long strings with no specific upper limit, use text or character varying without a length specifier, rather than making up an arbitrary length limit.
Related
I'd like to store this value efficiently in MSSQL 2016:
6d017ed2a48846f0ac025dd8603902c7
i.e, Fixed-length, ranging from 0 to f, hexidecimal, right?.
Char(32) seems too expensive.
Any kind of help would be appreciated. Thank you!
In almost all cases you shouldn't store this as a string at all. SQL Server has binary and varbinary types.
This string represents a 16-byte binary value. If the expected size is fixed, it can be stored as a binary(16). If the size changes, it can be stored as a varbinary(N) where N is the maximum expected size.
Don't use varbinary(max), that's meant to store BLOBs and has special storage and indexing characteristics.
Storing the string itself would make sense in few cases, eg if it's a hash string used in an API, or it's meant to be shown to humans. In this case, the data will always come as a string and will always have to be converted to a string to be used. In this case the constant conversions will probably cost more than the storage benefits.
I need to balance available disk space with the expected size of data. What sort of hit to storage occurs when there is unused space?
Example: "dog" being stored in nvarchar(10) vs nvarchar(100). If I plan for the worst, and choose nvarchar(100) instead of nvarchar(10), how much extra disk space is being wasted if I go with nvarchar(100)?
nvarchar storage size is 2 bytes per char + 2 extra bytes. The maximum length of the column doesn't matter - the storage size is determined by the actual data.
From official documentation:
nvarchar [ ( n | max ) ]
Variable-length Unicode string data. n defines the string length and can be a value from 1 through 4,000. max indicates that the maximum storage size is 2^30-1 characters. The maximum storage size in bytes is 2 GB. The actual storage size, in bytes, is two times the number of characters entered + 2 bytes. The ISO synonyms for nvarchar are national char varying and national character varying.
(emphasis mine)
However, Please do not consider this a recommendation to use nvarchar(max) for everything. Since max is treated differently, it has some nasty side effects (performance hits).
Generally speaking, you should choose the column max size by your estimated actual data size. To be on the safe side, you might want to simply set the max size twice the expected size.
If you know you are only going to use a single ASCII supported language, you should consider using varchar instead of nvarchar, since it's storage size is half the storage size of nvarchar:
varchar [ ( n | max ) ] Variable-length, non-Unicode string data. n defines the string length and can be a value from 1 through 8,000. max indicates that the maximum storage size is 2^31-1 bytes (2 GB). The storage size is the actual length of the data entered + 2 bytes. The ISO synonyms for varchar are charvarying or charactervarying
(Again, emphasis mine)
As far as I can remember and as Zohar has mentioned, there is very minimal difference in storage.
You will however, see potentially big impacts on query memory grants and therefore the overall performance of your server. As the Query Engine has no idea just how full those larger string columns actually are, it tries to allocate probably enough memory assuming many filled columns.
For further reading, go here.
I have a question in regards to data types that are available in SQL language to store data into the database itself. Since I'm dealing with database that is quite large, and has a tendency to expand over 150GB+ of data, I need to pay close attention and save up every bit of space on the server's hard drive so that the database doesn't takes up all the precious space. So my question is as following:
Which data type is the best to store 80-200 character long string in database?
I'm aware of for example varchar(200) and nvarchar(200) where the nvarchar supports unicode character. Which one of these would take up less space in database, or if there's a 3rd data type that I'm not aware of, and which I could use to store the data (if I know for a fact that the string I would store is just a combination of numbers and letters, without any special characters)
Are there some other techniques that I could use to save up space in database so that it doesn't expands rapidly ?
Can someone help me out with this ?
P.S. Guys, I have a 4th question as well:
If for example I have nvarchar(max) data type which is in a table, and the entered record takes up only 100 characters, how much data is reserved for that kind of record?
Let's say that I have ID which is of following form 191697193441 ... Would it make more sense to store this number as varchar(200) or bigint ?
The size needed for nvarchar is 2 bytes per character, as it represents unicode data. varchar needs 1 byte per character. The storage size is the actual number of characters entered + 2 bytes overhead. This is also true for varchar(max).
From https://learn.microsoft.com/en-us/sql/t-sql/data-types/char-and-varchar-transact-sql:
varchar [ ( n | max ) ] Variable-length, non-Unicode string data. n defines the string length and can be a value from 1 through 8,000. max indicates that the maximum storage size is 2^31-1 bytes (2 GB). The storage size is the actual length of the data entered + 2 bytes.
So for your 4th question, nvarchar would need 100 * 2 + 2 = 202 bytes, varchar would need 100 * 1 + 2 = 102 bytes.
There's no performance or data size difference as they're variable length data types, so they'll only use the space they need.
Think of the size parameter as more of a useful constraint. For e.g. if you have a surname field, you can reasonably expect 50 characters to be a sensible maximum size and you have more chance of a mistake (misuse of the field, incorrect data capture etc.) throwing an error, rather than adding nonsense to the database and needing future data cleansing.
So, my general rule of thumb is make them as large as the business requirements demand, but no larger. It's trivial to amend variable data sizes to a larger length in the future if requirements change.
I'm having trouble understanding how to define a column for my text that has the right size for my max. number of characters. In Oracle I can create a VARCHAR2(10 CHAR) which will be big enough for 10 characters. The size depends on the encoding used in the database. But how do I do that in SQL Server? Do I use varchar(10)? nvarchar(10)? I want to be able to store all kinds of characters (even chinese).
If you want Chinese characters, you need to use nvarchar(n) and specify a length of n that makes sense.
Those are characters you're defining, and the space you need is twice that number (since any Unicode character in SQL Server always uses 2 bytes).
Max. size is nvarchar(4000) - or if you really need more, use nvarchar(max) (for up to 1 billion characters).
I would recommend NOT to just use nvarchar(max) for everything, out of lazyness about considering what size you really need! Since it's a really large column, you won't be able to index it for one.
If you use nvarchar(max) this will allow for any number of characters for all character sets. The system will optimise storage.
Limitations on row size are addressed here. See answer from #marc_s for limitations on the use of max.
In sql server does it make a difference if I define a varchar column to be of length 32 or 128?
A varchar is a variable character field. This means it can hold text data to a certain length. A varchar(32) can only hold 32 characters, whereas a varchar(128) can hold 128 characters. If I tried to input "12345" into a varchar(3) field; this is the data that will be stored:
"123"
The "45" will be "truncated" (lost).
They are very useful in instances where you know that a certain field will only be (or only should be) a certain length at maximum. For example: a zip code or state abbreviation. In fact, they are generally used for almost all types of text data (such as names/addresses/et cetera) - but in these instances you must be careful that the number you supply is a sane maximum for the type of data that will fill that column.
However, you must also be careful when using them to only allow the user to input the maximum amount of characters that the field will support. Otherwise it may lend to confusion when it truncates the user's input.
There should be no noticeable difference as the backend will only store the amount of data you insert into that column. It's not padded out to the full size of the field like it is with a char column.
Edit: For more info, this link should be useful.
It should not. It just defines the maximum length it can accommodate, the actual used length depends on the data inserted.