- Make the code produce correct result: use an array of triggers to turn on/off equalities for each
  compared column. Also turn on/off optimizations based on those equalities.
- Make EXPLAIN output show "Full scan on NULL key" for tables for which we switch between
  ref/unique_subquery/index_subquery and ALL access.
- index_subquery engine now has HAVING clause when it is needed, and it is
  displayed in EXPLAIN EXTENDED
- Fix incorrect presense of "Using index" for index/unique-based subqueries (BUG#22930)
// bk trigger note: this commit refers to BUG#24127

When transforming "oe IN (SELECT ie ...)" wrap the pushed-down predicates
iff "oe can be null", not "ie can be null".
The fix doesn't cover row-based subqueries, those will be fixed in #24127.

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

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

2nd version
During tmp tables cleanup we get the handler for temporary table
and delete table using handler method.

In the method Item_field::fix_fields we try to resolve the name of
the field against the names of the aliases that occur in the select
list. This is done by a call of the function find_item_in_list.
When this function finds several occurrences of the field name
it sends an error message to the error queue and returns 0.
Yet the code did not take into account that find_item_in_list
could return 0 and tried to dereference the returned value.

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

used.

The Item::save_in_field() function is called from fill_record() to fill the 
new row with data while execution of the CREATE TABLE ... SELECT statement.
Item::save_in_field() calls val_xxx() methods in order to get values.
val_xxx() methods do not take into account the result field. Due to this
Item_func_set_user_var::val_xxx() methods returns values from the original
table, not from the temporary one.

The save_in_field() member function is added to the Item_func_set_user_var
class. It detects whether the result field should be used and properly updates
the value of the user variable.

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

A BINARY field is represented by the Field_string class. The space character
is used as the filler for unused characters in such a field. But a BINARY field 
should use \x00 instead.

Field_string:reset() now detects whether the current field is a BINARY one
and if so uses the \x00 character as a default value filler.

into  moonbone.local:/home/evgen/bk-trees/mysql-5.0-opt

into  olga.mysql.com:/home/igor/dev-opt/mysql-5.0-opt-bug25027

into  mysql.com:/d2/hf/opt/my50-opt

into  moonbone.local:/home/evgen/bk-trees/mysql-5.0-opt

into  olga.mysql.com:/home/igor/dev-opt/mysql-5.0-opt-bug24345

into  mysql.com:/d2/hf/opt/my50-opt

  The optimizer removes expressions from GROUP BY/DISTINCT
  if they happen to participate in a <expression> = <const>
  predicates of the WHERE clause (the idea being that if
  it's always equal to a constant it can't have multiple 
  values).
  However for predicates where the expression and the 
  constant item are of different result type this is not
  valid (e.g. a string column compared to 0).
  Fixed by additional check of the result types of the 
  expression and the constant and if they differ the 
  expression don't get removed from the group by list.

into  mysql.com:/d2/hf/opt/my50-opt

into  mysql.com:/d2/hf/opt/my50-opt

This bug appeared after the patch for bug 21390 that had added some code
to handle outer joins with no matches after substitution of a const
table in an efficient way. That code as it is cannot be applied to the case
of nested outer join operations. Being applied to the queries with
nested outer joins the code can cause crashes or wrong result sets.
The fix blocks row substitution for const inner tables of an outer join
if the inner operand is not a single table.  

into  rakia.gmz:/home/kgeorge/mysql/work/B15439-5.0-opt

  Addendum to the fix for bug#15439 : valgrind pb failed

into  mysql.com:/d2/hf/opt/my41-opt

into  mysql.com:/d2/hf/opt/my50-opt

into  mysql.com:/d2/hf/common/my50-common

into  mysql.com:/d2/hf/common/my50-common

into  mysql.com:/d2/hf/common/my50-common

into  mysql.com:/d2/hf/common/my50-common

  Temporary work around for bug#25359

into  mysql.com:/d2/hf/common/my50-common

into  mysql.com:/d2/hf/common/my41-common

into  mysql.com:/d2/hf/common/my50-common

into  mysql.com:/home/kent/bk/main/mysql-5.0