fulltext search was initialized for all MATCH ... AGAINST items
at the end of the JOIN::optimize(). But since 5.3 derived tables
are initialized lazily on first use, very late in the sub_select().
Skip Item_func_match::init_search initialization if the corresponding
table isn't open yet; repeat fulltext initialization for all
not-yet-initialized MATCH ... AGAINST items after creating derived tables.
init join->top_join_tab_count to be in sync with join->join_tab=stat,
otherwise a query can be killed in-between and join_tab's won't be deleted
(JOIN::cleanup won't call JOIN_TAB::cleanup)
One of them is quite serious: the function table_cond_selectivity used
the TABLE_REF structure for ref/eq_ref access methods as if they had been
filled. In fact these structure are filled after the best execution plan
has been chosen.
The other bugs happened due to:
- an erroneous attempt at get statistics on the result of materialization
of a view
- incorrect handling of ranges with no left/right limits when calculating
selectivity of range conditions on non-indexed columns
- lack of cleanup for some newly introduced fields
In some cases, when using views the optimizer incorrectly determined
possible join orders for queries with nested outer and inner joins.
This could lead to invalid execution plans for such queries.
RETURNS RANDOM DATA
MySQL 5.5 specific version of bugfix.
When Loose Index Scan Range access is used, MySQL execution needs
to copy non-aggregated fields. end_send() checked if this was
necessary by checking if join_tab->select->quick had type
QS_TYPE_GROUP_MIN_MAX.
In this bug, however, MySQL created a sort index to sort the rows
read from this range access method. create_sort_index() deletes
join_tab->select->quick which makes it impossible to inquire
the join_tab if LIS has been used.
The fix for MySQL 5.5 is to introduce a variable in JOIN_TAB
that stores whether or not LIS has been used. There is no need
for this variable in later MySQL versions because the relevant
code has been refactored.
This is a bug in the legacy code. It did not manifest itself because
it was masked by other bugs that were fixed by the patches for
mdev-4172 and mdev-4177.
This bug is a regression bug. The regression was introduced by
the patch for mdev-3851, that tried to weaken the condition when
a ref access with an extended key can be converted to an eq_ref
access. The patch incorrectly formed this condition. As a result,
while improving performance for some queries, the patch caused
worse performance for another queries.
Do not include BLOB fields into the key to access the temporary
table created for a materialized view/derived table.
BLOB components are not allowed in keys.
The function remove_eq_cond removes the parts of a disjunction
for which it has been proved that they are always true. In the
result of this removal the disjunction may be converted into a
formula without OR that must be merged into the the AND formula
that contains the disjunction.
The merging of two AND conditions must take into account the
multiple equalities that may be part of each of them.
These multiple equality must be merged and become part of the
and object built as the result of the merge of the AND conditions.
Erroneously the function remove_eq_cond lacked the code that
would merge multiple equalities of the merged AND conditions.
This could lead to confusing situations when at the same AND
level there were two multiple equalities with common members
and the list of equal items contained only some of these
multiple equalities.
This, in its turn, could lead to an incorrect work of the
function substitute_for_best_equal_field when it tried to optimize
ref accesses. This resulted in forming invalid TABLE_REF objects
that were used to build look-up keys when materialized subqueries
were exploited.
