The PROCEDURE clause of SELECT passes the whole result set to a Procedure
which will process it. These Procedures are not Stored Procedures, and can
only be written in the C language, so it is necessary to recompile the server.

Currently, the only available procedure is ANALYSE, which examines the
resultset and suggests the optimal datatypes for each column. It is defined in
the sql/sql_analyse.cc file, and can be used as an example to create more
Procedures.

This clause cannot be used in a view's definition.

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