BLOB is a binary large object that can hold a variable amount of data. The four
BLOB types are
LONGBLOB. These differ only in the maximum length of the values they can hold.
TEXT types are
LONGTEXT. These correspond to the four
and have the same maximum lengths and storage requirements. See Section
11.6, "Data Type Storage Requirements".
BLOB values are treated as binary strings (byte strings). They have no character
set, and sorting and comparison are based on the numeric values of the bytes in column values.
TEXT values are treated as nonbinary strings (character strings). They have a
character set, and values are sorted and compared based on the collation of the character set.
If strict SQL mode is not enabled and you assign a value to a
TEXT column that exceeds the column's maximum length, the value is truncated to fit
and a warning is generated. For truncation of nonspace characters, you can cause an error to occur (rather than
a warning) and suppress insertion of the value by using strict SQL mode. See Section
5.1.7, "Server SQL Modes".
Truncation of excess trailing spaces from values to be inserted into
TEXT columns always generates a warning, regardless of the SQL mode.
BLOB columns, there is no padding on
insert and no bytes are stripped on select.
TEXT column is indexed, index entry comparisons are space-padded at the end.
This means that, if the index requires unique values, duplicate-key errors will occur for values that differ
only in the number of trailing spaces. For example, if a table contains
attempt to store
'a ' causes a duplicate-key error. This is not true for
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 in the following ways:
If you use the
BINARY attribute with a
TEXT data type,
the column is assigned the binary collation of the column character set.
LONG VARCHAR map to the
data type. This is a compatibility feature.
MySQL Connector/ODBC defines
BLOB values as
TEXT values as
TEXT values can be extremely long,
you might encounter some constraints in using them:
Only the first
max_sort_length bytes of the column are used when sorting. The default
is 1024. You can make more bytes significant in sorting or grouping by increasing the value of
at server startup or runtime. Any client can change the value of its session
SET max_sort_length = 2000;mysql>
SELECT id, comment FROM t->
ORDER BY comment;
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 because the
MEMORY storage engine does
not support those data types (see Section
126.96.36.199, "How MySQL Uses Internal Temporary Tables"). Use of disk incurs a performance penalty,
TEXT columns in the query
result only if they are really needed. For example, avoid using
SELECT *, which selects all columns.
The maximum size of a
object is determined by its type, but the largest value you actually can transmit between the client and
server is determined by the amount of available memory and the size of the communications buffers. You
can change the message buffer size by changing the value of the
max_allowed_packet variable, but you must do so for both the server
and your client program. For example, both mysql and mysqldump enable you to change the client-side
value. See Section 8.11.2, "Tuning Server Parameters",
4.5.1, "mysql — The MySQL Command-Line Tool", and
4.5.4, "mysqldump — A Database Backup Program".
You may also want to compare the packet sizes and the size of the data objects you are storing with the
storage requirements, see Section 11.6, "Data Type
TEXT value is represented internally by a
separately allocated object. This is in contrast to all other data types, for which storage is allocated once
per column when the table is opened.
In some cases, it may be desirable to store binary data such as media files in
TEXT columns. You may find MySQL's string handling functions useful for working
with such data. See Section
12.5, "String Functions". For security and other reasons, it is usually preferable to do so using
application code rather than giving application users the
FILE privilege. You can discuss specifics for various languages and platforms
in the MySQL Forums (