account predicates that become sargable after reading const tables.
In some cases this resulted in choosing non-optimal execution plans.
Now info of such potentially saragable predicates is saved in
an array and after reading const tables we check whether this
predicates has become saragable.
strings
MySQL is setting the flag HA_END_SPACE_KEYS for all the keys that reference
text or varchar columns with collation different than binary.
This was done to handle correctly the situation where a lookup on such a key
may return more than 1 row because of the presence of many rows that differ
only by the amount of trailing space in the table's string column.
Inserting such values however appears to violate the unique checks on
INSERT/UPDATE. Thus that flag must not be set as it will prevent the optimizer
from choosing a faster access method.
This fix removes the setting of the HA_END_SPACE_KEYS flag.
After the patch for big 21698 equality propagation stopped
working for BETWEEN and IN predicates with STRING arguments.
This changeset completes the solution of the above patch.
while space allocation
Under some circumstances DISTINCT clause can be converted to grouping.
In such cases grouping is performed by all items in the select list.
If an ORDER clause is present then items from it is prepended to group list.
But the case with ORDER wasn't taken into account when allocating the
array for sum functions. This leads to memory corruption and crash.
The JOIN::alloc_func_list() function now allocates additional space if there
is an ORDER by clause is specified and DISTINCT -> GROUP BY optimization is
possible.
const tables. This resulted in choosing extremely inefficient
execution plans in same cases when distribution of data in
joined were skewed (see the customer test case for the bug).
- Make the range-et-al optimizer produce E(#table records after table
condition is applied),
- Make the join optimizer use this value,
- Add "filtered" column to EXPLAIN EXTENDED to show
fraction of records left after table condition is applied
- Adjust test results, add comments
When optimizing conditions like 'a = <some_val> OR a IS NULL' so that they're
united into a single condition on the key and checked together the server must
check which value is the NULL value in a correct way : not only using ->is_null
but also check if the expression doesn't depend on any tables referenced in the
current statement.
This additional check must be performed because that optimization takes place
before the actual execution of the statement, so if the field was initialized
to NULL from a previous statement the optimization would be applied incorrectly.
The problem was in that opt_sum_query() replaced MIN/MAX functions
with the corresponding constant found in a key, but due to imprecise
representation of float numbers, when evaluating the where clause,
this comparison failed.
When MIN/MAX optimization detects that all tables can be removed,
also remove all conjuncts in a where clause that refer to these
tables. As a result of this fix, these conditions are not evaluated
twice, and in the case of float number comparisons we do not discard
result rows due to imprecise float representation.
As a side-effect this fix also corrects an unnoticed problem in
bug 12882.
The problem was that when converting a string to an exact number,
rounding didn't work, because conversion didn't understand
approximate numbers notation.
Fix: a new function for string-to-number conversion was implemented,
which is aware of approxinate number notation (with decimal point
and exponent, e.g. -19.55e-1)
When an alias is set to a column leading spaces are removed from the alias.
But when this is done on aliases set by user this can lead to confusion.
Now Item::set_name() method issues the warning if leading spaces were removed
from an alias set by user.
New warning message is added.
Adding decimal "digits" in multiplication resulted in signed overflow and
producing wrong results.
Fixed by using large enough buffers and intermediary result types :
dec2 (currently longlong) to hold result of adding decimal "digits"
(currently int32).
Added test case for bug#18759 Incorrect string to numeric conversion.
select.test:
Added test case for bug#18759 Incorrect string to numeric conversion.
item_cmpfunc.cc:
Cleanup after fix for bug#18360 removal
The Field::eq() considered instances of Field_bit that differ only in
bit_ptr/bit_ofs equal. This caused equality conditions optimization
(build_equal_items_for_cond()) to make bad field substitutions that result
in wrong predicates.
Field_bit requires an overloaded eq() function that checks the bit_ptr/bit_ofs
in addition to Field::eq().
3.23 regression test failure
The member SEL_ARG::min_flag was not initialized,
due to which the condition for no GEOM_FLAG in function
key_or did not choose "Range checked for each record" as
the correct access method.
