Temporary table being created by outer statement
should not be visible to inner statement. And if
inner statement creates a table with same name.
The whole statement should fail with
ER_TABLE_EXISTS_ERROR.
Implemented by temporarily de-linking the TABLE_SHARE
being created by outer statement so that it remains
hidden to the inner statement.
mysqld maintains a list of TABLE objects for all temporary
tables created within a session in THD. Here each table is
represented by a TABLE object.
A query referencing a particular temporary table for more
than once, however, failed with ER_CANT_REOPEN_TABLE error
because a TABLE_SHARE was allocate together with the TABLE,
so temporary tables always had only one TABLE per TABLE_SHARE.
This patch lift this restriction by separating TABLE and
TABLE_SHARE objects and storing TABLE_SHAREs for temporary
tables in a list in THD, and TABLEs in a list within their
respective TABLE_SHAREs.
