Syntax:
PREPARE stmt_name FROM preparable_stmt

The PREPARE statement prepares a statement and assigns it a name,
stmt_name, by which to refer to the statement later. Statement names
are not case sensitive. preparable_stmt is either a string literal or a
user variable that contains the text of the statement. The text must
represent a single SQL statement, not multiple statements. Within the
statement, "?" characters can be used as parameter markers to indicate
where data values are to be bound to the query later when you execute
it. The "?" characters should not be enclosed within quotation marks,
even if you intend to bind them to string values. Parameter markers can
be used only where data values should appear, not for SQL keywords,
identifiers, and so forth.

If a prepared statement with the given name already exists, it is
deallocated implicitly before the new statement is prepared. This means
that if the new statement contains an error and cannot be prepared, an
error is returned and no statement with the given name exists.

A prepared statement is executed with EXECUTE and released with
DEALLOCATE PREPARE.

The scope of a prepared statement is the session within which it is
created. Other sessions cannot see it.

URL: http://dev.mysql.com/doc/refman/5.1/en/prepare.html

