Fixed incorrect checks in join_read_const_table() for when to
accept a non-existing, or empty const-row as a part of the const'ified
set of tables.
Intention of this test is to only accept NULL-rows if this table is outer joined
into the resultset. (In case of an inner-join we can conclude at this point that
resultset will be empty, end we want to return 'error' to signal this.)
Initially 'maybe_null' is set to the same value as 'outer_join' in
setup_table_map(), mysql_priv.h ~line 2424. Later simplify_joins() will
attemp to replace outer joins by inner join whenever possible. This
will cause 'outer_join' to be updated. However, 'maybe_null' is *not* updated
to reflect this rewrite as this field is used to currectly set the 'nullability'
property for the columns in the resultset.
We should therefore change join_read_const_table() to check the 'outer_join'
property instead of 'maybe_null', as this correctly reflect the nullability of
the *execution plan* (not *resultset*).
After the fix for
Bug #55077 Assertion failed: width > 0 && to != ((void *)0), file .\dtoa.c
we no longer try to allocate a string of length 'field_length'
so the asserts are relevant only for ZEROFILL columns.
from mysql-next-mr-opt-backporting.
Bug#54515: Crash in opt_range.cc::get_best_group_min_max on
SELECT from VIEW with GROUP BY
When handling the grouping items in get_best_group_min_max, the
items need to be of type Item_field. In this bug, an ASSERT
triggered because the item used for grouping was an
Item_direct_view_ref (i.e., the group column is from a view).
The fix is to get the real_item since Item_ref* pointing to
Item_field is ok.
file .\filesort.cc, line 149 (part II)
Problem: the server didn't disregard sort order
for some zero length tuples.
Fix: skip sort order in such a case
(zero length NOT NULL string functions).
All numeric operators and functions on integer, floating point
and DECIMAL values now throw an 'out of range' error rather
than returning an incorrect value or NULL, when the result is
out of supported range for the corresponding data type.
Some test cases in the test suite had to be updated
accordingly either because the test case itself relied on a
value returned in case of a numeric overflow, or because a
numeric overflow was the root cause of the corresponding bugs.
The latter tests are no longer relevant, since the expressions
used to trigger the corresponding bugs are not valid anymore.
However, such test cases have been adjusted and kept "for the
record".
column is used for ORDER BY
Problem: filesort isn't meant for null length sort data
(e.g. char(0)), that leads to a server crash.
Fix: disregard sort order if sort data record length is 0 (nothing
to sort).
NULLable BIGINT and INT columns in comparison
Problem: a consequence of the fix for 43668.
Some Arg_comparator inner initialization missed,
that may lead to unpredictable (wrong) comparison
results.
Fix: always properly initialize Arg_comparator
before its usage.
Arg_comparator uses Item_cache objects to store constants being compared when
they're need a type conversion. Because this cache wasn't initialized properly
Arg_comparator might produce wrong comparison result.
The Arg_comparator::cache_converted_constant function now initializes cache
prior to usage.
field='const1' AND field='const2' in some cases
Building multiple equality predicates containing
a constant which is compared as a datetime (with a field)
we should take this fact into account and compare the
constant with another possible constatns as datetimes
as well.
E.g. for the
SELECT ... WHERE a='2001-01-01' AND a='2001-01-01 00:00:00'
we should compare '2001-01-01' with '2001-01-01 00:00:00' as
datetimes but not as strings.
Constant expressions in WHERE/HAVING/ON clauses aren't cached and evaluated
for each row. This causes slowdown of query execution especially if constant
UDF/SP function are used.
Now WHERE/HAVING/ON expressions are analyzed in the top-bottom direction with
help of the compile function. When analyzer meets a constant item it
sets a flag for the tree transformer to cache the item and doesn't allow tree
walker to go deeper. Thus, the topmost item of a constant expression if
cached. This is done after all other optimizations were applied to
WHERE/HAVING/ON expressions
A helper function called cache_const_exprs is added to the JOIN class.
It calls compile method with caching analyzer and transformer on WHERE,
HAVING, ON expressions if they're present.
The cache_const_expr_analyzer and cache_const_expr_transformer functions are
added to the Item class. The first one check if the item can be cached and
the second caches it if so.
A new Item_cache_datetime class is derived from the Item_cache class.
It caches both int and string values of the underlying item independently to
avoid DATETIME aware int-to-string conversion. Thus it completely relies on
the ability of the underlying item to correctly convert DATETIME value from
int to string and vice versa.
init_read_record() - (records.cc:274)
Item_cond::used_tables_cache was accessed in
records.cc#init_read_record() without being initialized. It had
not been initialized because it was wrongly assumed that the
Item's variables would not be accessed, and hence
quick_fix_field() was used instead of fix_fields() to save a few
CPU cycles at creation time.
The fix is to properly initilize the Item by replacing
quick_fix_field() with fix_fields().
memory
The server was doing a bad class typecast causing setting of
wrong value for the maximum number of items in an internal
structure used in equality propagation.
Fixed by not doing the wrong typecast and asserting the type
of the Item where it should be done.
subquery returning multiple rows
Error handling was missing when handling subqueires in WHERE
and when assigning a SELECT result to a @variable.
This caused crash(es).
Fixed by adding error handling code to both the WHERE
condition evaluation and to assignment to an @variable.
line 138 when forcing a spatial index
Problem: "Spatial indexes can be involved in the search
for queries that use a function such as MBRContains()
or MBRWithin() in the WHERE clause".
Using spatial indexes for JOINs with =, <=> etc.
predicates is incorrect.
Fix: disable spatial indexes for such queries.
The TABLE::reginfo.impossible_range is used by the optimizer to indicate
that the condition applied to the table is impossible. It wasn't initialized
at table opening and this might lead to an empty result on complex queries:
a query might set the impossible_range flag on a table and when the query finishes,
all tables are returned back to the table cache. The next query that uses the table
with the impossible_range flag set and an index over the table will see the flag
and thus return an empty result.
The open_table function now initializes the TABLE::reginfo.impossible_range
variable.
Bug #40925: Equality propagation takes non indexed attribute
Query execution plans and execution time of queries like
select a, b, c from t1
where a > '2008-11-21' and b = a limit 10
depended on the order of equality operator parameters:
"b = a" and "a = b" are not same.
An equality propagation algorithm has been fixed:
the substitute_for_best_equal_field function should not
substitute a field for an equal field if both fields belong
to the same table.
select where .. (col=col and col=col) or ... (false expression)
Problem: optimizer didn't take into account a singular case
when we eliminated all the predicates at the AND level of WHERE.
That may lead to wrong results.
Fix: replace (a=a AND a=a...) with TRUE if we eliminated all the
predicates.
Table could be marked dependent because it is
either 1) an inner table of an outer join, or 2) it is a part of
STRAIGHT_JOIN. In case of STRAIGHT_JOIN table->maybe_null should not
be assigned. The fix is to set st_table::maybe_null to 'true' only
for those tables which are used in outer join.
Field_varstring::store
The code that temporary saved the bitmaps of the read set and the write set so that
it can set it to all columns for debug purposes was not expecting that the
table->read_set and table->write_set can be the same. And was always saving both in
sequence.
As a result the original value was never restored.
Fixed by saving & restoring the original value only once if the two sets are the
same (in a special set of functions).
Problem is not about intervals and doesn't actually cause 'full table scan'.
We have an optimization for DISTINCT when we have
'DISTINCT field_from_first_join_table' we don't need to read all the
rows from the JOIN-ed table if we found one conforming row.
It stopped working in 5.0 as we return NESTED_LOOP_OK if we came upon
that case in the evaluate_join_record() and that doesn't break the
recordreading loop in sub_select().
Fixed by returning NESTED_LOOP_NO_MORE_ROWS in this case.
type conversion.
Instead of copying of whole character string from a temporary
buffer, the server copied a short-living pointer to that string
into a long-living structure. That has been fixed.
Comparison of a BIGINT NOT NULL column with a constant arithmetic
expression that evaluates to NULL caused error 1048: "Column '...'
cannot be null".
Made convert_constant_item() check if the constant expression is NULL
before attempting to store it in a field. Attempts to store NULL in a
NOT NULL field caused query errors.
