PROCEDURE clause of SELECT passes the whole result set to a Procedure which will process it. Those Procedures are not Stored Procedures. They can only be written in 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.