Analysis:
The wrong result is a consquence of sorting the subquery
result and then selecting only the first row due to the
artificial LIMIT 1 introduced by the fix_fields phase.
Normally, if there is an ORDER BY in a subquery, the ORDER
is removed (Item_in_subselect::select_in_like_transformer),
however if a GROUP BY is transformed into ORDER, this happens
later, after the removal of the ORDER clause of subqueries, so
we end up with a subquery with an ORDER clause, and an artificially
added LIMIT 1.
The reason why the same works in the main 5.3 without MWL#89, is
that the 5.3 performs all subquery transformations, including
IN->EXISTS before JOIN::optimize(). The beginning of JOIN::optimize
does:
if (having || (select_options & OPTION_FOUND_ROWS))
select_limit= HA_POS_ERROR;
which sets the limit back to infinity, thus 5.3 sorts the whole
subquery result, and IN performs the lookup into all subquery result
rows.
Solution:
Sorting of subqueries without LIMIT is meaningless. Since LIMIT in
subqueries is not supported, the patch removes sorting by setting
join->skip_sort_order= true
for each subquery JOIN object. This improves a number of execution
plans to not perform unnecessary sorting at all.
Before sorting HAVING condition is split into two parts,
first part is a table related condition and the rest of is
HAVING part. Extraction of HAVING part does not take into account
the fact that some of conditions might be non-const but
have 'used_tables' == 0 (independent subqueries)
and because of that these conditions are cut off by
make_cond_for_table() function.
The fix is to use (table_map) 0 instead of used_tables in
third argument for make_cond_for_table() function.
It allows to extract elements which belong to sorted
table and in addition elements which are independend
subqueries.
mysql-test/r/having.result:
test case
mysql-test/t/having.test:
test case
sql/sql_select.cc:
The fix is to use (table_map) 0 instead of used_tables in
third argument for make_cond_for_table() function.
It allows to extract elements which belong to sorted
table and in addition elements which are independend
subqueries.
Valgrind warnings were caused by comparing index values to an un-initialized field.
mysql-test/r/subselect.result:
New test cases.
mysql-test/t/subselect.test:
New test cases.
sql/opt_sum.cc:
Add thd to opt_sum_query enabling it to test for errors.
If we have a non-nullable index, we cannot use it to match null values,
since set_null() will be ignored, and we might compare uninitialized data.
sql/sql_select.cc:
Add thd to opt_sum_query, enabling it to test for errors.
sql/sql_select.h:
Add thd to opt_sum_query, enabling it to test for errors.
There are two problems with ANALYSE():
1. Memory leak
it happens because do_select() can overwrite
JOIN::procedure field(with zero value in our case) and
JOIN destructor don't free the memory allocated for
JOIN::procedure. The fix is to save original JOIN::procedure
before do_select() call and restore it after do_select
execution.
2. Wrong result
If ANALYSE() procedure is used for the statement with LIMIT clause
it could retrun empty result set. It happens because of missing
analyse::end_of_records() call. First end_send() function call
returns NESTED_LOOP_QUERY_LIMIT and second call of end_send() with
end_of_records flag enabled does not happen. The fix is to return
NESTED_LOOP_OK from end_send() if procedure is active.
mysql-test/r/analyse.result:
test case
mysql-test/t/analyse.test:
test case
sql/sql_select.cc:
--save original JOIN::procedure before do_select() call and
restore it after do_select execution.
--return NESTED_LOOP_OK from end_send() if procedure is active
- "Using MRR" is no longer shown with range access.
- Instead, both range and BKA accesses will show one of the following:
= "Rowid-ordered scan"
= "Key-ordered scan"
= "Key-ordered Rowid-ordered scan"
depending on whether DS-MRR implementation will do scan keys in order, rowids in order,
or both.
- The patch also introduces a way for other storage engines/MRR implementations to
pass information to EXPLAIN output about the properties of employed MRR scans.
- Auto-merge with 5.3 main.
- Changed the test for LP BUG#719198 so that
an two more queries were added, and removed a
query that produces a wrong result due to an
unrelated problem. The wrong result is submitted
as a separate bug.
Fixed memory leak from HEAP tables that was not deleted properly
BUILD/compile-alpha-ccc:
Use g++ instead of gcc for linking
BUILD/compile-alpha-debug:
Use g++ instead of gcc for linking
BUILD/compile-pentium-pgcc:
Use g++ instead of gcc for linking
BUILD/compile-solaris-sparc:
Use g++ instead of gcc for linking
BUILD/compile-solaris-sparc-debug:
Use g++ instead of gcc for linking
BUILD/compile-solaris-sparc-purify:
Use g++ instead of gcc for linking
sql/item.cc:
Safety fixes for expr_cache
Call Item_result:field::cleanup() in Item_cache_wrapper::cleanup()
More DBUG_PRINT
sql/sql_base.cc:
Simple optimization for setup_wild
More DBUG_PRINT
sql/sql_expression_cache.cc:
Added header
Removed not needed initialization
sql/sql_lex.cc:
More DBUG_PRINT
sql/sql_select.cc:
More DBUG_PRINT
Fixed memory leak from HEAP tables that was not deleted properly
storage/heap/hp_create.c:
More DBUG_PRINT
Analysis:
There are two code paths through which JOIN::exec may produce
an all-NULL row for an empty result set. One goes via the
function return_zero_rows(), when query processing detectes
early that the where clause is false, the other one is via
do_select() in the case of join execution.
In the case of do_select(), the problem was that the executioner
didn't set TABLE::null_row to 1. As result when sending the only
result row, the evaluation of each field didn't detect that all
non-aggregated fields are NULL, because Field::is_null returned
true, after checking that field->table->null_row was false.
Given that the each non-aggregated field was not considered NULL,
select_result::send_data sent whatever was in the buffer of each
field. However, since there was no actual data in the field buffer,
send_data() accessed and sent whatever junk was in the field's
data buffer.
Solution:
Similar to the analogous case in return_zero_rows() mark all
tables that their current row is NULL before sending the
artificailly created NULL row.
Analysis:
A query with implicit grouping is one with aggregate functions and
no GROUP BY clause. MariaDB inherits from MySQL an SQL extenstion
that allows mixing aggregate functions with non-aggregate fields.
If a query with such mixed select clause produces an empty result
set, the meaning of aggregate functions is well defined - either
NULL (MIN, MAX, etc.), or 0 (count(*)). However the non-aggregated
fields must also have some value, and the only reasonable value in
the case of empty result is NULL.
The cause of the many wrong results was that if a field is declared
as non-nullable (e.g. because it is a PK or NOT NULL), the semantic
analysis and the optimization phases treat this field as non-nullable,
and generate all related query plan elements based on this assumption.
Later during execution, these incorrectly configured/generated query
plan elements result in a wrong result because the selected fields
are not null due to the not-null assumption during optimization.
Solution:
Detect before the context analysys phase that a query uses implicit
grouping with mixed aggregates/non-aggregates, and set all fields
as nullable. The parser already walks the SELECT clause, and
already sets Item::with_sum_func for Items that reference aggreagate
functions. The patch adds a symmetric Item::with_field so that all
Items that reference an Item_field are marked during their
construction at parse time in the same way as with aggregate function
use.
mysql-test/r/union.result:
Added test for lp:732124
mysql-test/t/union.test:
Added test for lp:732124
sql/sp_rcontext.cc:
Updated function definition for ::send_data()
sql/sp_rcontext.h:
Updated function definition for ::send_data()
sql/sql_analyse.cc:
Test if send_data() returned an error
sql/sql_class.cc:
Updated function definition for ::send_data()
sql/sql_class.h:
Changed select_result::send_data(List<Item> &items) to return -1 in case of duplicate row that should not be counted as part of LIMIT
sql/sql_cursor.cc:
Check if send_data returned error
sql/sql_delete.cc:
Updated function definition for ::send_data()
sql/sql_insert.cc:
Updated function definition for ::send_data()
sql/sql_select.cc:
Don't count rows which send_data() tells you to ignore
sql/sql_union.cc:
Inform caller that the row should be ignored. This is the real bug fix for lp:732124
sql/sql_update.cc:
Updated function definition for ::send_data()
This allows us to simplify and speed up some tests and also remove get_cached_item()
sql/item.h:
Added item.real_type()
Removed get_cached_item()
sql/opt_range.cc:
Simplify test
sql/sql_select.cc:
Simplify test
sql/sql_show.cc:
Simplify test
If join condition is of the form <t2.key>=<t1.no_key> then the server
performs no index look-ups when looking for matching rows of t2 for
the rows from t1 with t1.no_key=NULL. It happens because the function
add_not_null_conds() injects an additional condition of the form
IS NOT NULL(<t1.no_key>) into the WHERE condition.
However if the join condition was of the form <t.key>=<outer_ref> no
additional null rejecting predicate was generated. This could lead
to extra records in the result set if the value of <outer_ref> happened
to be NULL.
The new code injects null rejecting predicates of the form
IS NOT NULL(<outer_ref>) and evaluates them before the first row
the subquery is constructed.
