Description
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A BLOB is a binary large object that can hold a variable amount of data. The
four BLOB types are

* TINYBLOB,
* BLOB, 
* MEDIUMBLOB, and
* LONGBLOB.

These differ only in the maximum length of the values they can hold.

The TEXT types are

* TINYTEXT,
* TEXT,
* MEDIUMTEXT, and
* LONGTEXT.
* JSON (alias for LONGTEXT)

These correspond to the four BLOB types and have the same maximum lengths and
storage requirements.

MariaDB starting with 10.2.1
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Starting from MariaDB 10.2.1, BLOB and TEXT columns can have a DEFAULT value.

MariaDB starting with 10.4.3
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From MariaDB 10.4, it is possible to set a unique index on columns that use
the BLOB or TEXT data types.

URL: https://mariadb.com/kb/en/blob-and-text-data-types/