Syntax
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MEDIUMTEXT [CHARACTER SET charset_name] [COLLATE collation_name]

Description
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A TEXT column with a maximum length of 16,777,215 (224 - 1) characters. The
effective maximum length is less if the value contains multi-byte characters.
Each MEDIUMTEXT value is stored using a three-byte length prefix that
indicates the number of bytes in the value.

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