This performance degradation for UPDATEs could be observed in the update
statements for which the search key cannot be converted to any valid
value of the type of the search column, like for a  the condition
int_fld=99999999999999999999999999, though it can be guaranteed here
that there is no row with such a key value. 

additional call of file->extra() method with HA_EXTRA_NO_CACHE parameter

into  rakia.gmz:/home/kgeorge/mysql/autopush/B23556-5.0-opt

  merge of the 5.0-opt tree

into  rakia.gmz:/home/kgeorge/mysql/autopush/B23556-5.0-opt

into  rakia.gmz:/home/kgeorge/mysql/autopush/B25551-5.0-opt

The bug could cause choosing a sub-optimal execution plan for 
a single-table query if a unique index with many null keys were 
defined for the table. 
It happened because the code of the check_quick_keys function 
made an assumption that any key may occur in an unique index 
only once. Yet this is not true for keys with nulls that may 
have multiple occurrences in the index.

into  olga.mysql.com:/home/igor/mysql-5.0-opt

into  mysql.com:/home/hf/work/25973/my50-25973

into  rakia.gmz:/home/kgeorge/mysql/autopush/B25575-5.0-opt

 Two problems here:

 Problem 1:

 While constructing the join columns list the optimizer does as follows:
  1. Sets the join_using_fields/natural_join members of the right JOIN 
   operand.
  2. Makes a "table reference" (TABLE_LIST) to parent the two tables.
  3. Assigns the join_using_fields/is_natural_join of the wrapper table
   using join_using_fields/natural_join of the rightmost table
  4. Sets join_using_fields to NULL for the right JOIN operand.
  5. Passes the parent table up to the same procedure on the upper 
   level.

 Step 1 overrides the the join_using_fields that are set for a nested 
 join wrapping table in step 4.
 Fixed by making a designated variable SELECT_LEX::prev_join_using to 
 pass the data from step 1 to step 4 without destroying the wrapping 
 table data.

 Problem 2:

 The optimizer checks for ambiguous columns while transforming 
 NATURAL JOIN/JOIN USING to JOIN ON. While doing that there was no
 distinction between columns that are used in the generated join
 condition (where ambiguity can be checked) and the other columns
 (where ambiguity can be checked only when resolving references
 coming from outside the JOIN construct itself).
 Fixed by allowing the non-USING columns to be present in multiple 
 copies in both sides of the join and moving the ambiguity check 
 to the place where unqualified references to the join columns are
 resolved (find_field_in_natural_join()).

 The optimizer takes away columns from GROUP BY/DISTINCT if they constitute
 all the parts of an unique index.
 However if some of the columns can contain NULLs this cannot be done 
(because an UNIQUE index can have multiple rows with NULL values).
 Fixed by not using UNIQUE indexes with nullable columns to remove
 grouping columns from GROUP BY/DISTINCT.

into  olga.mysql.com:/home/igor/dev-opt/mysql-5.0-opt-bug24987

Made the function opt_sum_query to return HA_ERR_KEY_NOT_FOUND when
no matches were found (instead of -1 it returned prior this patch).
This changes allow us to avoid possible conflicts with return values
from user-defined handler methods which also may return -1. 
No particular test cases are provided with this fix.

into  rakia.gmz:/home/kgeorge/mysql/autopush/B25643-5.0-opt

 Checking for NULL before calling the val_xxx()
 methods only checks for such arguments that are 
 known to be NULLs at compile time. 
 The arguments that may or may not contain
 NULLs (e.g. function calls and possibly others)
 are not checked at all.
 Fixed by first calling the val_xxx() method and
 then checking for null in SEC_TO_TIME().
 In addition QUARTER() was not returning 0 (as all the 
 val_int() functions do when processing a NULL value).

Objects of the classes Item_func_is_not_null_test and Item_func_trig_cond
must be transparent for the method Item::split_sum_func2 as these classes
are pure helpers. It means that the method Item::split_sum_func2 should
look at those objects as at pure wrappers.

into  olga.mysql.com:/home/igor/dev-opt/mysql-5.0-opt-bug24653

into  mysql.com:/home/gluh/MySQL/Merge/5.0

into  olga.mysql.com:/home/igor/dev-opt/mysql-5.0-opt-bug24653

The bug report has demonstrated the following two problems.
1. If an ORDER/GROUP BY list includes a constant expression being 
optimized away and, at the same time, containing single-row
subselects that return more that one row, no error is reported.
Strictly speaking the standard allows to ignore error in this case.
Yet, now a corresponding fatal error is reported in this case.
2. If a query requires sorting by expressions containing single-row
subselects that, however, return more than one row, then the execution
of the query may cause a server crash. 
To fix this some code has been added that blocks execution of a subselect
item in case of a fatal error in the method Item_subselect::exec.

into  mockturtle.local:/home/dlenev/src/mysql-5.0-merge

into  mysql.com:/home/psergey/mysql-5.0-bug8804-r12

Fixed typo problem that surfaced after the merge

into  mysql.com:/home/svoj/devel/mysql/merge/mysql-5.0-engines

into  mysql.com:/home/svoj/devel/mysql/merge/mysql-5.0-engines

identical pushed_cond_guards arrays. Allocate only one always.

the team tree for additional investigation.

into  mockturtle.local:/home/dlenev/src/mysql-5.0-merge

into  mysql.com:/home/psergey/mysql-5.0-bug8804-r12

into  mysql.com:/home/gluh/MySQL/Merge/5.0-opt

into  chilla.local:/home/mydev/mysql-5.0-bug24607

After merge fix

into  chilla.local:/home/mydev/mysql-5.0-bug24607

Fixed test. On 32-bit machines which compile without
-DBIG_TABLES, MAX_ROWS is truncated to a 32-bit value.
Using a value below 4G is portable.

into  kahlann.erinye.com:/home/df/mysql/build/mysql-5.0-build-work

into  mysql.com:/home/svoj/devel/mysql/BUG24401/mysql-5.0-engines