I was wondering if you where to have an article or articles with huge amounts of text, what would be better when creating the database structure for the articles text? And why?
What will be the advantages or disadvantages if any?.
I was thinking of using one of the data types below to hold the articles text for the MySQL database.
VARCHAR
TEXT
MEDIUMTEXT
LONGTEXT
Please have a look at the Documentation of MySQL, there're the differences between these types explained.
But to answer your question, VARCHAR is a field of user-defined length, while the Text-Fields have a system-defined size:
VarChar [1-whatever (max at 65535)]
TinyText 255 (2^8 - 1)
Text 65535 (2^16 - 1)
MediumText 16M (2^24 - 1)
LongText 4G (2^32 - 1)
So, I use VarChar whenever I need a field which is smaller then 255.
For longer chunks of text, TEXT is a good choice. If you want the full text search features, be sure to set an index of FULLTEXT on the field. This will require a table in the MyISAM format. You can read more here: http://dev.mysql.com/doc/refman/5.1/en/fulltext-search.html
An important difference between VARCHAR and TEXT fields is how they are stored.
VARCHAR fields are stored in the row its self and so the MySQL maximum row size limit of 65,535 bytes applies.
TEXT fields are stored separately so they can potentially be huge, but this also means an additional step when reading them making them slower.
My suggestion would be to always use VARCHAR for small amounts of text and reserve TEXT for when you need to store substantial amounts.
If you do use TEXT fields make sure to exclude them from your SELECT queries unless you need them as this will make the queries faster.
Related
I've got a messages table in MySQL which records messages between users. Apart from the typical ids and message types (all integer types) I need to save the actual message text as either VARCHAR or TEXT. I'm setting a front-end limit of 3000 characters which means the messages would never be inserted into the db as longer than this.
Is there a rationale for going with either VARCHAR(3000) or TEXT? There's something about just writing VARCHAR(3000) that feels somewhat counter-intuitive. I've been through other similar posts on Stack Overflow but would be good to get views specific to this type of common message storing.
TEXT and BLOB may by stored off the table with the table just having a pointer to the location of the actual storage. Where it is stored depends on lots of things like data size, columns size, row_format, and MySQL version.
VARCHAR is stored inline with the table. VARCHAR is faster when the size is reasonable, the tradeoff of which would be faster depends upon your data and your hardware, you'd want to benchmark a real-world scenario with your data.
Can you predict how long the user input would be?
VARCHAR(X)
Max Length: variable, up to 65,535 bytes (64KB)
Case: user name, email, country, subject, password
TEXT
Max Length: 65,535 bytes (64KB)
Case: messages, emails, comments, formatted text, html, code, images, links
MEDIUMTEXT
Max Length: 16,777,215 bytes (16MB)
Case: large json bodies, short to medium length books, csv strings
LONGTEXT
Max Length: 4,294,967,29 bytes (4GB)
Case: textbooks, programs, years of logs files, harry potter and the goblet of fire, scientific research logging
There's more information on this question.
Just to clarify the best practice:
Text format messages should almost always be stored as TEXT (they end up being arbitrarily long)
String attributes should be stored as VARCHAR (the destination user name, the subject, etc...).
I understand that you've got a front end limit, which is great until it isn't. *grin* The trick is to think of the DB as separate from the applications that connect to it. Just because one application puts a limit on the data, doesn't mean that the data is intrinsically limited.
What is it about the messages themselves that forces them to never be more then 3000 characters? If it's just an arbitrary application constraint (say, for a text box or something), use a TEXT field at the data layer.
Short answer: No practical, performance, or storage, difference.
Long answer:
There is essentially no difference (in MySQL) between VARCHAR(3000) (or any other large limit) and TEXT. The former will truncate at 3000 characters; the latter will truncate at 65535 bytes. (I make a distinction between bytes and characters because a character can take multiple bytes.)
For smaller limits in VARCHAR, there are some advantages over TEXT.
"smaller" means 191, 255, 512, 767, or 3072, etc, depending on version, context, and CHARACTER SET.
INDEXes are limited in how big a column can be indexed. (767 or 3072 bytes; this is version and settings dependent)
Intermediate tables created by complex SELECTs are handled in two different ways -- MEMORY (faster) or MyISAM (slower). When 'large' columns are involved, the slower technique is automatically picked. (Significant changes coming in version 8.0; so this bullet item is subject to change.)
Related to the previous item, all TEXT datatypes (as opposed to VARCHAR) jump straight to MyISAM. That is, TINYTEXT is automatically worse for generated temp tables than the equivalent VARCHAR. (But this takes the discussion in a third direction!)
VARBINARY is like VARCHAR; BLOB is like TEXT.
A table with several 'large' VARCHARs could hit a limit of 64KB for the whole table definition; switching to TEXT is a simple and practical fix. (Example: (42000) Row size too large, from an Oracle dump to a MySQL dump )
Rebuttal to other answers
The original question asked one thing (which datatype to use); the accepted answer answered something else (off-record storage). That answer is now out of date.
When this thread was started and answered, there were only two "row formats" in InnoDB. Soon afterwards, two more formats (DYNAMIC and COMPRESSED) were introduced.
The storage location for TEXT and VARCHAR() is based on size, not on name of datatype. For an updated discussion of on/off-record storage of large text/blob columns, see this .
Disclaimer: I'm not a MySQL expert ... but this is my understanding of the issues.
I think TEXT is stored outside the mysql row, while I think VARCHAR is stored as part of the row. There is a maximum row length for mysql rows .. so you can limit how much other data you can store in a row by using the VARCHAR.
Also due to VARCHAR forming part of the row, I suspect that queries looking at that field will be slightly faster than those using a TEXT chunk.
The preceding answers don't insist enough on the main problem: even in very simple queries like
(SELECT t2.* FROM t1, t2 WHERE t2.id = t1.id ORDER BY t1.id)
a temporary table can be required, and if a VARCHAR field is involved, it is converted to a CHAR field in the temporary table. So if you have in your table say 500 000 lines with a VARCHAR(65000) field, this column alone will use 6.5*5*10^9 byte. Such temp tables can't be handled in memory and are written to disk. The impact can be expected to be catastrophic.
Source (with metrics): https://nicj.net/mysql-text-vs-varchar-performance/
(This refers to the handling of TEXT vs VARCHAR in "standard"(?) MyISAM storage engine. It may be different in others, e.g., InnoDB.)
Varchar is for small data like email addresses, while Text is for much bigger data like news articles, Blob for binary data such as images.
The performance of Varchar is more powerful because it runs completely from memory, but this will not be the case if data is too big like varchar(4000) for example.
Text, on the other hand, does not stick to memory and is affected by disk performance, but you can avoid that by separating text data in a separate table and apply a left join query to retrieve text data.
Blob is much slower so use it only if you don't have much data like 10000 images which will cost 10000 records.
Follow these tips for maximum speed and performance:
Use varchar for name, titles, emails
Use Text for large data
Separate text in different tables
Use Left Join queries on an ID such as a phone number
If you are going to use Blob apply the same tips as in Text
This will make queries cost milliseconds on tables with data >10 M and size up to 10GB guaranteed.
There is a HUGE difference between VARCHAR and TEXT. While VARCHAR fields can be indexed, TEXT fields cannot. VARCHAR type fields are stored inline while TEXT are stored offline, only pointers to TEXT data is actually stored in the records.
If you have to index your field for faster search, update or delete than go for VARCHAR, no matter how big. A VARCHAR(10000000) will never be the same as a TEXT field bacause these two data types are different in nature.
If you use you field only for archiving
you don't care about data
speed retrival
you care about speed but you will use the operator
'%LIKE%' in your search query so indexing will not help much
you
can't predict a limit of the data length
than go for TEXT.
Just a correction to so many answers here, even if it is a bit late to the party.
Text fields can be fully indexed by MySQL as per their documentation.
Link provided
https://dev.mysql.com/doc/refman/5.6/en/column-indexes.html
Overall Varchar fields are longer to write to then Text fields, but it only matters if you have multitude of write requests
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
MySQL: Large VARCHAR vs. TEXT?
Since VARCHAR can have 65k bytes now, when then should TEXT be used instead of VARCHAR?
A long VARCHAR is stored in the same manner as a TEXT/BLOB field in InnoDB.
From storage prospective BLOB, TEXT as
well as long VARCHAR are handled same
way by Innodb. This is why Innodb
manual calls it “long columns” rather
than BLOBs.
source
Unless you need to index these columns (in which case VARCHAR is much faster) there is no reason to use VARCHAR over TEXT for long fields - there are some engine specific optimisations in MySQL to tune the data retrieval according to length, and you should use the correct column type to take advantage of these.
In case you're using MyISAM an in-depth discussion on the topic is here.
TEXT and BLOB are stored off the table with the table just having a pointer to the location of the actual storage.
VARCHAR is stored inline with the table. VARCHAR is faster when the size is reasonable.
According to this test, VARCHAR is about thrice as fast as text.
Text should be used for really long strings of indeterminate length. Also, queries that return TEXT fields tend to be much slower than their VARCHAR counterparts.
We have a very large historical table that contains a column with at most 500 UTF8 characters, and the disk space grows really fast!
We're having at least 2 million rows a day... and we were wondering which would do a better job (mostly in storage but in performance as well)? TEXT or VARCHAR(512)?
VARCHAR is probably preferable in your case from both the storage and performance perspective. View this oft-reposted article.
This is useful information; I think in general, the answer is the varchar is usually the better bet.
From the MySQL manual:
In most respects, you can regard a
BLOB column as a VARBINARY column that
can be as large as you like.
Similarly, you can regard a TEXT
column as a VARCHAR column. BLOB and
TEXT differ from VARBINARY and VARCHAR
in the following ways:
There is no trailing-space removal for BLOB and TEXT columns when values
are stored or retrieved. Before MySQL
5.0.3, this differs from VARBINARY and VARCHAR, for which trailing spaces are
removed when values are stored.
On comparisons, TEXT is space extended to fit the compared object,
exactly like CHAR and VARCHAR.
For indexes on BLOB and TEXT columns, you must specify an index
prefix length. For CHAR and VARCHAR, a
prefix length is optional. See Section
7.5.1, “Column Indexes”.
BLOB and TEXT columns cannot have DEFAULT values.
http://dev.mysql.com/doc/refman/5.0/en/blob.html
I noticed that in MySQL, both VARCHAR and TEXT offer variable-sized data. Well, VARCHAR is a bit more efficient in data storage, but still, TEXT MEDIUMTEXT and LONGTEXT offer a lot more potential. So, what are the real uses of VARCHAR?
First of all, you should read the 10.4. String Types section of the MySQL's manual : it'll give you all the informations you are looking for :
10.4.1. The CHAR and VARCHAR Types
10.4.3. The BLOB and TEXT Types
A couple of important differences :
Difference in the amount of text those can contain :
varchar have a quite small size limit ; with the newest versions of MySQL, it's 64 KB, for the total of all varchar columns of a row -- which is not that much.
TEXT have virtually no limit, as they can contain something like 2^32 bytes.
There are differences in indexing and sorting, if I'm not mistake ; quoting the page about TEXT :
About sorting : "Only the first max_sort_length bytes of the column are used when sorting."
And, about performances : "Instances of BLOB or TEXT columns in the result of a query that is processed using a temporary table causes the server to use a table on disk rather than in memory"
Considering these informations, if you are sure that your strings will not be too long, and that you'll always be able to store them in a varchar, I would use a varchar.
This question is based on two things performance and size
Which DATATYPE is better to use TEXT or VARCHAR? Based on performance which will affect and which will impove?
It depends on what you're using it for. I hate to give such a generic answer, but it's true. Generally, try to get the data type as specific as you can. If your strings will never exceed some upper limit of characters, then go with VARCHAR because it will be a little more efficient. If you need more space, go with TEXT. If you aren't sure how much space your text will take up, you should probably go with TEXT; the performance difference isn't very large, and it's better to be future-proof than risk having to change it later when your requirements change. Just my two cents.
In the comments, Pitarou points out that, if MySQL creates a temporary table for your query (see this), TEXT columns will not be stored in memory and will have to be read from the disk, which is much slower. (Source, bottom of the page.) This shouldn't matter for most queries, though.
In case anyone was wondering how PostgreSQL compares, I found this benchmark that shows that CHAR, VARCHAR, and TEXT all perform equally well. So if you're using Postgres, it doesn't matter what type you use.
From V 5.0.3 onwards, Limit of VARCHAR is increased from 0-256 to 0-65,535 (subject to the maximum row size (65,535 bytes, which is shared among all columns) and the character set used.)
Ref. http://dev.mysql.com/doc/refman/5.0/en/char.html
If you are using TEXT that is fixed 64k length, even if you required lesser limit
So Better to go with VARCHAR with higher limit than TEXT.
If requirement is more than 64K go with MEDIUMTEXT or LONGTEXT accordingly.
Queries against the TEXT table were always 3 times slower than those against the VARCHAR table (averages: 0.10 seconds for the VARCHAR table, 0.29 seconds for the TEXT table). The difference is 100% repeatable.
Benchmark from http://forums.mysql.com/read.php?24,105964,105964
VARCHAR you can set a limit for how many chars it will accept per record, text is (virtually) unlimited... not exactly sure about performance, but i would assume a more specific datatype (varchar) would be faster.
VARCHAR should have a better performance since it has a limited size. In fact, in all of my experiences with MySQL, the search operation was always faster with VARCHAR than TEXT. Anyway, it's based on my experience. You should check the documentation to find out more about it.
It really depends on your data type.
If your field is fixed-length (e.g. a 32-character hash value), then use CHAR. This has better performance because every entry takes up the same space per row.
The standard limit for VARCHAR was 255 characters but I think it's been increased now. TEXT is pretty damn long and is generally only used for big content like a whole blog post, and comments if you don't want a limit.
With regard to size there is no (or very little) difference between VARCHAR and TEXT since they just store what they need to. CHAR fields will always take up their allotted length.
Performance-wise, VARCHAR is usually faster. VARCHARs can be indexed too which leads to faster searching.
MySQL will internally convert TEXT to varchar while creating temporary tables. So it is better to use VARCHAR if possible. There are a few minor bugs related to TEXT column such as...
http://bugs.mysql.com/bug.php?id=36676
As per my Opinion VARCHAR is best option when u know the length of characters. It will also reduce garbage Memory Allocations and space issue. TEXT will consume 255 where as VARCHAR will consume as u give the values to it.
As per performance, VARCHAR is also faster then TEXT.
There is a subtle difference in text and varchar. I have a table as shown:
CREATE TABLE `test`.`tbl`(
`kee` BIGINT UNSIGNED NOT NULL AUTO_INCREMENT,
`txt` TEXT(100),
`vrchr` VARCHAR(100),
PRIMARY KEY (`kee`)
);
I insert a row:
INSERT INTO `tbl`
(`txt`,
`vrchr`)
VALUES ('1
2
3',
'1
2
3');
The column txt has value:
1
2
3
and column vrchr has value:
1