ROLLUP is defined as the UNION of grouping by every prefix of fields in
the original GROUP BY list. A ROLLUP query with an empty result set
returned zero rows when it should return a summary NULL, since grouping
by the empty prefix returns a single summary row.
The empty row case is handled in two separate locations. First, if the
optimizer is able to determine that no rows will be produced, e.g. due
to the table being empty or the WHERE condition resolving to false,
JOIN::send_row_on_empty_set is used to determine whether or not to send
an empty result row. Therefore, send_row_on_empty_set is modified to
include select_lex->olap == ROLLUP_TYPE.
Second, it may be the case that the absence of rows is not confirmed
until the execution phase. For instance when the WHERE condition is not
constant, or in the case of InnoDB where an empty table is not detected
during optimization. This is handled in both end_send_group and
end_write_group by this expression
join->first_record ||
(end_of_records && !join->group && !join->group_optimized_away)
The condition is extracted into need_empty_set_row and a second variable
empty_set_send_rollup_total is recorded to prevent running the default
rollup_send_data/rollup_write_data on the empty row case. This is
because the null summary row is already handled by send_data_with_check.
Remove the unscoped #pragma GCC diagnostic ignored
"-Wdeprecated-declarations" from include/violite.h and replace all
sprintf/vsprintf calls with snprintf/vsnprintf across the codebase.
Where possible, pass actual buffer sizes as function parameters
instead of using hardcoded constants or recomputing strlen().
Notable API changes:
- get_date(): added to_len parameter for buffer size
- nice_time(), end_timer() in client/mysql.cc: added buff_size
- generate_new_name(): added name_size parameter
- calc_md5(): added buffer_size parameter (fixes off-by-one)
- MD5_HASH_TO_STRING macro: added _size parameter
- Added MYSQL_UDF_MAX_RESULT_LENGTH constant in mysql_com.h
Also fixed a pre-existing bug in sql/rpl_mi.cc where the ellipsis
"..." was written to the wrong buffer (dbuff instead of buff).
Vendored code is excluded: extra/readline, extra/wolfssl,
wsrep-lib, libmariadb, storage/mroonga/vendor, zlib.
Affected functions:
find_matching_field_pair(Item *item, List<Field_pair> pair_list)
get_corresponding_field_pair(Item *item, List<Field_pair> pair_list)
Both only traverse the pair_list.
They use List_iterator so we can't easily switch to using const-reference.
ft_handler isn't getting initialized for subqueries inside explain
delete/update queries. However, ft_handler is accessed inside ha_ft_read(),
and is the reason for NULL pointer exception.
This is not the case with non-explain delete/update queries, as
well as explain/non-explain select queries.
Follow the approach the SELECT statements are using in
JOIN::optimize_constant_subqueries(): remove SELECT_DESCRIBE
flag when invoking optimization of constant subqueries.
Single-table UPDATE/DELETEs have SELECT_LEX but don't have JOIN.
So, we make optimize_constant_subqueries() not to be a member
of JOIN class, and instead move it to SELECT_LEX, and then
invoke it from single-table UPDATE/DELETE as well as for SELECT queries.
Rename cloning methods of class Item and its descendants
in the following way:
(from) (to)
do_build_clone -> deep_copy
build_clone -> deep_copy_with_checks
do_get_copy -> shallow_copy
get_copy -> shallow_copy_with_checks
to better reflect their functionality.
Also make Item::deep_copy() and shallow_copy() protected.
Outside users should call deep_copy_with_checks()
and shallow_copy_with_checks().
Fix rownum in HAVING clause or subquery
Description
==========
When rownum used in HAVING without GROUP BY, accepted_rows should be
incremented even if the having cond's value is 0.
When rownum used in subquery
1. Forbid subquery transformed to semi join.
2. New conditions must be added into having clause when doing in2exists.
When processing a degenerate JTBM semi-join (a subquery that produces
0 or 1 rows), `execute_degenerate_jtbm_semi_join()` creates equality
conditions and adds them to `eq_list`. These equalities are then merged
with existing conditions via `and_new_conditions_to_optimized_cond()`,
creating an `Item_cond_and`.
When multiple conditions need to be combined, a new `Item_cond_and` is
created and populated. However, this item was not fixed before being
walked by the `is_simplified_cond_processor`, which calls `val_bool()`
to check if the condition is a known constant. Calling `val_bool()`
on an unfixed item triggers the assertion.
Solution:
Fix the newly created `Item_cond_and` immediately after it's populated
ensuring it's ready for any subsequent operations including evaluation.
- Removed duplicate words, like "the the" and "to to"
- Removed duplicate lines (one double sort line found in mysql.cc)
- Fixed some typos found while searching for duplicate words.
Command used to find duplicate words:
egrep -rI "\s([a-zA-Z]+)\s+\1\s" | grep -v param
Thanks to Artjoms Rimdjonoks for the command and pointing out the
spelling errors.
The code in best_access_path() uses PREV_BITS(uint, N) to
compute a bitmap of all keyparts: {keypart0, ... keypart{N-1}).
The problem is that PREV_BITS($type, N) macro code can't handle the case
when N=<number of bits in $type).
Also, why use PREV_BITS(uint, ...) for key part map computations when
we could have used PREV_BITS(key_part_map) ?
Fixed both:
- Change PREV_BITS(type, N) to handle any N in [0; n_bits(type)].
- Change PREV_BITS() to use key_part_map when computing key_part_map bitmaps.
Improve performance of queries like
SELECT * FROM t1 WHERE field = NAME_CONST('a', 4);
by, in this example, replacing the WHERE clause with field = 4
in the case of ref access.
The rewrite is done during fix_fields and we disambiguate this
case from other cases of NAME_CONST by inspecting where we are
in parsing. We rely on THD::where to accomplish this. To
improve performance there, we change the type of THD::where to
be an enumeration, so we can avoid string comparisons during
Item_name_const::fix_fields. Consequently, this patch also
changes all usages of THD::where to conform likewise.
The code inside Item_subselect::fix_fields() could fail to check
that left expression had an Item_row, like this:
(('x', 1.0) ,1) IN (SELECT 'x', 1.23 FROM ... UNION ...)
In order to hit the failure, the first SELECT of the subquery had
to be a degenerate no-tables select. In this case, execution will
not enter into Item_in_subselect::create_row_in_to_exists_cond()
and will not check if left_expr is composed of scalars.
But the subquery is a UNION so as a whole it is not degenerate.
We try to create an expression cache for the subquery.
We create a temp.table from left_expr columns. No field is created
for the Item_row. Then, we crash when trying to add an index over a
non-existent field.
Fixed by moving the left_expr cardinality check to a point in
check_and_do_in_subquery_rewrites() which gets executed for all
cases.
It's better to make the check early so we don't have to care about
subquery rewrite code hitting Item_row in left_expr.
This bug affected EXPLAIN EXTENDED command for single-table DELETE that
used an IN subquery in its WHERE clause. A crash happened if the optimizer
chose to employ index_subquery or unique_subquery access when processing
such command.
The crash happened when the command tried to print the transformed query.
In the current code of 10.4 for single-table DELETE statements the output
of any explain command is produced after the join structures of all used
subqueries have been destroyed. JOIN::destroy() sets the field tab of the
JOIN_TAB structures created for subquery tables to NULL. As a result
subselect_indexsubquery_engine::print(), subselect_indexsubquery_engine()
cannot use this field to get the alias name of the joined table.
This patch suggests to use the field TABLE_LIST::TAB that can be accessed
from JOIN_TAB::tab_list to get the alias name of the joined table.
Approved by Oleksandr Byelkin <sanja@mariadb.com>
This patch also fixes some bugs detected by valgrind after this
patch:
- Not enough copy_func elements was allocated by Create_tmp_table() which
causes an memory overwrite in Create_tmp_table::add_fields()
I added an ASSERT() to be able to detect this also without valgrind.
The bug was that TMP_TABLE_PARAM::copy_fields was not correctly set
when calling create_tmp_table().
- Aria::empty_bits is not allocated if there is no varchar/char/blob
fields in the table. Fixed code to take this into account.
This cannot cause any issues as this is just a memory access
into other Aria memory and the content of the memory would not be used.
- Aria::last_key_buff was not allocated big enough. This may have caused
issues with rtrees and ma_extra(HA_EXTRA_REMEMBER_POS) as they
would use the same memory area.
- Aria and MyISAM didn't take extended key parts into account, which
caused problems when copying rec_per_key from engine to sql level.
- Mark asan builds with 'asan' in version strihng to detect these in
not_valgrind_build.inc.
This is needed to not have main.sp-no-valgrind fail with asan.
The problem was that federated engine does not support comparable rowids
which was not taken into account by semijoin code.
Fixed by checking that we don't use semijoin with tables that does not
support comparable rowids.
Other things:
- Fixed some typos in the code comments
Replaced Cost_estimate prefix_cost with a double as prefix_cost was
only used to store and retrive total prefix cost.
This also speeds up things (a bit) as don't have to call
Cost_estimate::total_cost() for every access to the prefix_cost.
Sizeof POSITION decreased from 304 to 256.
optimize_semi_joins() calls update_sj_state() to update semi-join
optimization state in the JOIN class.
greedy_search() algorithm considers different join prefixes,
and then picks one table to put into the join prefix.
Most of the semi-join optimization state is in the table's entry
in the join->positions[cur_prefix_size].
However, it also needs to call update_sj_state() to update the
semi-join optimization state in the JOIN class.
There is one exception, which is the cause of this bug: when we're
inside optimize_semi_join_nests() and are optimizing a subquery,
optimize_semi_joins() does nothing, it doesn't call update_sj_state().
greedy_search() must not do that either.
