MDEV-32640 Reset thd->lex->mi.connection_name.str towards the end of mysql_execute_command
Reset the connection_name to contain a null string, if the pointer
points to the same space as that of the system variable
default_master_connection.
We do this because the system variable may be updated which could free
the pointer and create a new one, causing use-after-free for
re-execution of prepared statements and stored procedures where the
LEX may be reused.
This allows connection_name to be set again be to the system variable
pointer in the next call of this function (see earlier in this
function), after any possible updates to the system variable.
MDEV-34085 Server crash ASAN used-after-poison upon 2nd execution of PS with erroneous timestamp conversion
The optimization code replacing DATETIME comparison to TIMESTAMP comparison
in conditions like:
- WHERE timestamp_col=const_expr
- WHERE const_expr IN (SELECT timestamp_column FROM t1)
worked as follows:
- Install an internal condition handler (suppressing and counting warnings).
- Convert const_expr from its data type to TIMESTAMP
- Check the warning count collected by the internal condition handler:
* If any warnings happened during the constant conversion,
then continue with DATETIME comparison.
* Otherwise, go to the next stage of switching to TIMESTAMP comparison.
This scenario did not take into account that in some cases warnings
are escalated to errors. Errors were not caught by the internal handler,
so Type_handler_datetime_common::convert_item_for_comparison()
returned with an SQL error in the diagnostics area.
The calling code did not expect this.
Fixing the code to suppress and count both errors and warnings, to make sure
Type_handler_datetime_common::convert_item_for_comparison() returns without
adding any errors to DA if the conversion to TIMESTAMP fails and it decides
to go with DATETIME comparison.
