Syntax
------ 
BLOB[(M)]
 
Description
----------- 
A BLOB column with a maximum length of 65,535 (216 - 1)
bytes. Each
BLOB value is stored using a two-byte length prefix that
indicates the
number of bytes in the value.
 
An optional length M can be given for this type. If this is
done,
MariaDB creates the column as the smallest BLOB type large
enough to
hold values M bytes long.
 
BLOBS can also be used to store dynamic columns.
 
Before MariaDB 10.2.1, BLOB and TEXT columns could not be
assigned a DEFAULT value. This restriction was lifted in
MariaDB 10.2.1.
 
Indexing
 
In MariaDB 10.4, it is possible to set a Unique index on a
column that uses the BLOB data type. In previous releases
this was not possible, as the index would only guarantee the
uniqueness of a fixed number of characters.
 
Oracle Mode
 
In Oracle mode from MariaDB 10.3, BLOB is a synonym for
LONGBLOB.
 


URL: https://mariadb.com/kb/en/blob/