if this matters, i also set it unique
The max I've managed to set for varchar is 745 (it's set to unique also).
Depends what version of MySQL you are running, before 5.0.3 there was a 255 character limit for varchar:
Values in VARCHAR columns are
variable-length strings. The length
can be specified as a value from 0 to
255 before MySQL 5.0.3, and 0 to
65,535 in 5.0.3 and later versions.
From: http://dev.mysql.com/doc/refman/5.0/en/char.html
Update:
Maybe it has to do with the maximum key length of 1000 bytes:
The maximum key length is 1000 bytes. This can also be changed by changing the source and recompiling. For the case of a key longer than 250 bytes, a larger key block size than the default of 1024 bytes is used.
As an index is created for the key and as it is working without an index, this makes sense.
Nevertheless you can have an index on varchar columns bigger than 1000 bytes as you can read in my answer below.
Or if you are using InnoDB, then there are some restrictions:
Index key prefixes can be up to 767 bytes. See Section 12.1.8, “CREATE INDEX Syntax”.
I assume it is to ensure that the index doesn't get too large and works acceptable fast.
If it is very likely that a string column has a unique prefix on the first number of characters, it is better to index only this prefix, using MySQL's support for creating an index on the leftmost part of the column (see Section 12.1.8, “CREATE INDEX Syntax”). Shorter indexes are faster, not only because they require less disk space, but because they also give you more hits in the index cache, and thus fewer disk seeks. See Section 7.5.3, “Tuning Server Parameters”.
That means also that you can define the first n characters of such a column that should get indexed. Maybe this helps to circumvent the problem.
Example:
CREATE INDEX part_of_name ON customer (name(10));
Old mysql?
5 and newer can use long varchar
http://dev.mysql.com/doc/refman/5.0/en/char.html
Values in VARCHAR columns are
variable-length strings. The length
can be specified as a value from 0 to
255 before MySQL 5.0.3, and 0 to
65,535 in 5.0.3 and later versions.
The effective maximum length of a
VARCHAR in MySQL 5.0.3 and later is
subject to the maximum row size
(65,535 bytes, which is shared among
all columns) and the character set
used.
A small visit around the MySQL manual should be useful:
http://dev.mysql.com/doc/refman/5.0/en/char.html
Values in VARCHAR columns are variable-length strings. The length can be specified as a value from 0 to 255 before MySQL 5.0.3, and 0 to 65,535 in 5.0.3 and later versions. The effective maximum length of a VARCHAR in MySQL 5.0.3 and later is subject to the maximum row size (65,535 bytes, which is shared among all columns) and the character set used.
An additional:
Key values length can't exceed 500 characters. (Reported as of http://bugs.mysql.com/bug.php?id=2130)
Next step up in length would probably be text, though as far as I know that has some really huge in-database length limit, if any, so you'd have to provide limits in the programming sql/backend application logic.
Related
I need to create column in mysql 5.1 that can store user's feedback.
It shouldn't be too long, so I think not more 1000 characters of UTF-8.
The question is how to represent this efficiently in mysql 5.1.
For now I have:
`description` varchar NOT NULL,
But how to constrain varchar to hold at most 1000 characters of UTF-8?
From the documentation:
Values in VARCHAR columns are variable-length strings. The length can be specified as a value from 0 to 255 before MySQL 5.0.3, and 0 to 65,535 in 5.0.3 and later versions. The effective maximum length of a VARCHAR in MySQL 5.0.3 and later is subject to the maximum row size (65,535 bytes, which is shared among all columns) and the character set used.
This means that you can store up to 65,535 bytes in a VARCHAR column. However, from the String Type Overview:
MySQL interprets length specifications in character column definitions in character units. (Before MySQL 4.1, column lengths were interpreted in bytes.) This applies to CHAR, VARCHAR, and the TEXT types.
So, declare your table with a UTF8 collation and set the length of the varchar to 1,000 characters and MySQL will do the work for you behind the scenes.
Since the size is apparently defined in bytes, ...
-correction- Field size is defined in 'character units'. It's a bit unclear what they mean by that, but I guess they mean 'code units'.
Removed the rest of the detailed explanation, since it wasn't (entirely true).
Correction. In MySQL you actually define the number of characters in the field. It is still limited to the 65535 byte boundary though. Above that, MySQL just reserves 3 bytes per character for UTF-8, which means that you cannot have UTF-8 fields of more than 21844 characters, and declaring a field als VARCHAR(21900) will just fail for that reason: " Column length too big for column 'field1' (max = 21845); use BLOB or TEXT instead: ". The number in this message is wrong, by the way. The actual maximum size is 21844. 21845 is 1/3 of 65535, but I guess you need to subtract the two bytes for the field size header as well.
The limit of 3 bytes is weird, though. The unicode definition is designed to be able to expand with extra characters. There are already supplementary characters of 4 bytes, that actually cannot be stored in a UTF-8 varchar(1) field, or any varchar field for that matter, since MySQL just doesn't seem able to read those characters: "Incorrect string value: '\xF0\xA0\x9C\x8E' for column 'field1' at row 1". So I guess you would need an actual binary/blob column to be able to store these characters.
I think the documentation about this subject is pretty poor, but I've tried some things and came to this conclusion. You can see the fiddle here: http://sqlfiddle.com/#!2/4d938
To the question:
So for your specific situation, declaring the field as varchar(1000) will do the trick, presuming you don't want people to use the supplementary characters in their feedback.
Some things to consider though:
I think a 'feedback' field of 1000 characters is pretty small. For many folks this will be enough, but if you have to say more, it is annoying if you can't. So I would make the field bigger.
varchar fields are stored in the record and consume a part of the maximum row size of 65536 bytes. This is an important fact. You cannot have two varchar(20000) fields in a row, because together they would be larger than this maximum row size.
A better alternative for large text fields would be therefor be to make them TEXT or MEDIUMTEXT, which can be even larger and are stored in a different way.
Values in VARCHAR columns are variable-length strings. The length can be specified as a value from 0 to 255 before MySQL 5.0.3, and 0 to 65,535 in 5.0.3 and later versions.
http://dev.mysql.com/doc/refman/5.0/en/char.html
I would like to know what the max size is for a MySQL VARCHAR type.
I read that the max size is limited by the row size which is about 65k. I tried setting the field to varchar(20000) but it says that that's too large.
I could set it to varchar(10000). What is the exact max I can set it to?
Keep in mind that MySQL has a maximum row size limit
The internal representation of a MySQL table has a maximum row size limit of 65,535 bytes, not counting BLOB and TEXT types. BLOB and TEXT columns only contribute 9 to 12 bytes toward the row size limit because their contents are stored separately from the rest of the row. Read more about Limits on Table Column Count and Row Size.
Maximum size a single column can occupy, is different before and after MySQL 5.0.3
Values in VARCHAR columns are variable-length strings. The length can be specified as a value from 0 to 255 before MySQL 5.0.3, and 0 to 65,535 in 5.0.3 and later versions. The effective maximum length of a VARCHAR in MySQL 5.0.3 and later is subject to the maximum row size (65,535 bytes, which is shared among all columns) and the character set used.
However, note that the limit is lower if you use a multi-byte character set like utf8 or utf8mb4.
Use TEXT types inorder to overcome row size limit.
The four TEXT types are TINYTEXT, TEXT, MEDIUMTEXT, and LONGTEXT. These correspond to the four BLOB types and have the same maximum lengths and storage requirements.
More details on BLOB and TEXT Types
Ref for MySQLv8.0 https://dev.mysql.com/doc/refman/8.0/en/blob.html
Ref for MySQLv5.7 https://dev.mysql.com/doc/refman/5.7/en/blob.html
Ref for MySQLv5.6 https://dev.mysql.com/doc/refman/5.6/en/blob.html
Even more
Checkout more details on Data Type Storage Requirements which deals with storage requirements for all data types.
As per the online docs, there is a 64K row limit and you can work out the row size by using:
row length = 1
+ (sum of column lengths)
+ (number of NULL columns + delete_flag + 7)/8
+ (number of variable-length columns)
You need to keep in mind that the column lengths aren't a one-to-one mapping of their size. For example, CHAR(10) CHARACTER SET utf8 requires three bytes for each of the ten characters since that particular encoding has to account for the three-bytes-per-character property of utf8 (that's MySQL's utf8 encoding rather than "real" UTF-8, which can have up to four bytes).
But, if your row size is approaching 64K, you may want to examine the schema of your database. It's a rare table that needs to be that wide in a properly set up (3NF) database - it's possible, just not very common.
If you want to use more than that, you can use the BLOB or TEXT types. These do not count against the 64K limit of the row (other than a small administrative footprint) but you need to be aware of other problems that come from their use, such as not being able to sort using the entire text block beyond a certain number of characters (though this can be configured upwards), forcing temporary tables to be on disk rather than in memory, or having to configure client and server comms buffers to handle the sizes efficiently.
The sizes allowed are:
TINYTEXT 255 (+1 byte overhead)
TEXT 64K - 1 (+2 bytes overhead)
MEDIUMTEXT 16M - 1 (+3 bytes overhead)
LONGTEXT 4G - 1 (+4 bytes overhead)
You still have the byte/character mismatch (so that a MEDIUMTEXT utf8 column can store "only" about half a million characters, (16M-1)/3 = 5,592,405) but it still greatly expands your range.
Source
The max length of a varchar is subject to the max row size in MySQL,
which is 64KB (not counting BLOBs):
VARCHAR(65535) However, note that the limit is lower if you use a
multi-byte character set:
VARCHAR(21844) CHARACTER SET utf8
From MySQL documentation:
The effective maximum length of a VARCHAR in MySQL 5.0.3 and later is
subject to the maximum row size (65,535 bytes, which is shared among
all columns) and the character set used. For example, utf8 characters
can require up to three bytes per character, so a VARCHAR column that
uses the utf8 character set can be declared to be a maximum of 21,844
characters.
Limits for the VARCHAR varies depending on charset used. Using ASCII would use 1 byte per character. Meaning you could store 65,535 characters. Using utf8 will use 3 bytes per character resulting in character limit of 21,844. BUT if you are using the modern multibyte charset utf8mb4 which you should use! It supports emojis and other special characters. It will be using 4 bytes per character. This will limit the number of characters per table to 16,383. Note that other fields such as INT will also be counted to these limits.
Conclusion:
utf8 maximum of 21,844 characters
utf8mb4 maximum of 16,383 characters
you can also use MEDIUMBLOB/LONGBLOB or MEDIUMTEXT/LONGTEXT
A BLOB type in MySQL can store up to 65,534 bytes, if you try to store more than this much data MySQL will truncate the data. MEDIUMBLOB can store up to 16,777,213 bytes, and LONGBLOB can store up to 4,294,967,292 bytes.
Before Mysql version 5.0.3 Varchar datatype can store 255 character, but from 5.0.3 it can be store 65,535 characters.
BUT it has a limitation of maximum row size of 65,535 bytes. It means including all columns it must not be more than 65,535 bytes.
In your case it may possible that when you are trying to set more than 10000 it is exceeding more than 65,535 and mysql will gives the error.
For more information: https://dev.mysql.com/doc/refman/5.0/en/column-count-limit.html
blog with example: http://sforsuresh.in/mysql_varchar_max_length/
In my case, I tried 20'000 according to #Firze answer (with UTF8 limit) and phpMyAdmin responded with the maximum size; the answer was to decrease or choose BLOB instead.
So, I think, finally, the best is to test yourself according to the version of MySQL you have and the engine used. As MySQL / phpMyAdmin has safeguards.
You can use TEXT type, which is not limited to 64KB.
Regarding innodb, someone recently told me:
"the varchar content beyond 768 bytes
is stored in supplemental 16K pages"
This is very interesting. If each varchar will be latin1, which I believe stores as 1byte per letter, would a single varchar(500) (<768 bytes) require an extra i/o as a varchar(1000) (>768 bytes) would??
(this question is to find out if all varchars or just big varchars are split into a separate page)
Is the 768 limit per varchar or for all varchars in the row added together? (for example, does this get optimized - varchar(300), varchar(300), varchar(300): [where each individual varchar column is below 768 but together they are above 768 characters]?
I am confused about if the 768 limit relates to each individual varchar or all varchars in the row totaled (as in the question). Any clarification?
EDIT: Removed part about CHARS due to finding out about their limit of 255 max.
The documentation of the current MySQL does not mention this constraint. It actually gives the impression that VARCHAR is stored in the row itself, as the sum of the length of all VARCHARs together in a row cannot be more than 65k bytes.
It also mentions that storage is length+data, which is different from what you describe.
I did find a mention of a splitted storage in MySQL compression internals:
Tables created in previous versions of
InnoDB use the “Antelope” file format,
which supports only
ROW_FORMAT=REDUNDANT and
ROW_FORMAT=COMPACT. In these formats,
InnoDB stores the first 768 bytes of
BLOB, VARCHAR and TEXT columns in the
clustered index record along with the
primary key. The 768-byte prefix is
followed by a 20-byte pointer to the
overflow pages that contain the rest
of the column value.
To me this suggests that each column is considered individually when determining whether that column needs an overflow.
This seems to contrast with newer versions of MySQL which seem to store VARCHAR quite differently. A VARCHAR in a newer version has a max length of 65k bytes, which seems to be stored in the record iself (no overflow), which results in the constraint that all columns together may not be longer than 65k byte.
a CHAR is very different. It's maximum length is 255, and it is stored in the row itself. So no CHAR(500) :)
The length of a CHAR column is fixed
to the length that you declare when
you create the table. The length can
be any value from 0 to 255. When CHAR
values are stored, they are
right-padded with spaces to the
specified length. When CHAR values are
retrieved, trailing spaces are removed
unless the PAD_CHAR_TO_FULL_LENGTH SQL
mode is enabled.
My server has my SQL version of 5.0.91-community, now i have to store a long string of approx about 500 character more or less, i thought of going with text data type but then someone told me it slows the performance, i wanted to know more about varchar and it's limit.
i used to think that varchar is only limited to 255 characters, but then i read it somewhere it is capable of storing more then that in the newer version i.e >= 5.0.3 , as i am using 5.0.91 what do you think i should use? if i use it like varchar(1000) is it still valid?
thank you.
The documentation is here,
varchar has a max size of 65,535 in MySQL 5.0.3 and later , before 5.0.3 the limit was 255
Note that the effective size is less,
The effective maximum length of a
VARCHAR in MySQL 5.0.3 and later is
subject to the maximum row size
(65,535 bytes, which is shared among
all columns) and the character set
used.
You have to specify the max size, e.g. varchar(1000). Just stating varchar isn't enough.
From The CHAR and VARCHAR Types
Values in VARCHAR columns are
variable-length strings. The length
can be specified as a value from 0 to
65,535. The effective maximum length
of a VARCHAR is subject to the maximum
row size (65,535 bytes, which is
shared among all columns) and the
character set used.
According to the MySQL doc:
TEXT differs from VARCHAR in the following ways:
There is no trailing-space removal for TEXT columns when values are stored or retrieved. Before MySQL 5.0.3, this differs from VARCHAR, for which trailing spaces are removed when values are stored.
For indexes on TEXT columns, you must specify an index prefix length. For CHAR and VARCHAR, a prefix length is optional.
TEXT columns cannot have DEFAULT values.
Apart from these differences, using VARCHAR like using TEXT, so the question of size is not what should make you choose between those two, unless you really need to store no more characters than 1000.
In MySQL, VARCHAR accepts maximum of 65535 chars.
You can assure yourself very easy. Mysql documentation is openly accessed and it says
Values in VARCHAR columns are variable-length strings. The length can be specified as a value from 0 to 255 before MySQL 5.0.3, and 0 to 65,535 in 5.0.3 and later versions
as for the performance issues, it doesn't matter. Not data type but data relations affect performance.
If I have a column in table with field of type VARCHAR(15) and if I try to insert data of length 16, MySQL gives an error stating
Data too long for column 'testname' at row 1
Does anyone know why VARCHAR fields in MySQL take fixed length? Also how many bytes does a VARCHAR field take per record based on the size given?
From the MySQL 5.0 Manual:
Values in VARCHAR columns are variable-length strings. The length can be specified as a value from 0 to 255 before MySQL 5.0.3, and 0 to 65,535 in 5.0.3 and later versions. The effective maximum length of a VARCHAR in MySQL 5.0.3 and later is subject to the maximum row size (65,535 bytes, which is shared among all columns) and the character set used.
I only use VARCHAR when I'm certain that the data the column needs to hold will never exceed a certain length, and even then I'm cautious. If I'm storing a text string I tend to use one of the TEXT types.
Check out the MySQL Storage Requirements for more information on how the bytes are used.
If you set a column to be varchar(15) the maximum bytes allowed is 15. Thus you can't pass it more than 15 characters without modifying the column to support more than 15. If you store a 4 character string it should only use around 4 bytes out of a possible 15, whereas if you used char(15) it would have filled in the other 11 with empty bytes.
http://dev.mysql.com/doc/refman/5.0/en/char.html
( My byte calculation was probably off since it's always -1/+1 or something like that ).
Small extra local note. The number of bytes used will depend on the encoding scheme in use. 1 byte per character in latin1 encoding, but up to 3 in UTF8. See link in mlambie's answer for details.
If you look here it should tell you everything about varchar you want to know:
http://dev.mysql.com/doc/refman/5.0/en/char.html
Basically, depending on the length you chose it will use 1 or two bytes to track the length of the current string in that column, so it will store the number of bytes for the data you put in, plus one or two bytes.
So, if you put in 'abc' then it will be 4 or 5 bytes used for that column in that row.
If you used char(15) then even 'abc' would take up 15 bytes, as the data is the right-padded to use up the full 15 bytes.