sql/filesort.cc:
Snippet of filesort() code moved to function reuse_freed_buff() -
change buffpek pointers to use buff from freed BUFFPEK
Used in filesort() and merge_walk().
sql/item_sum.cc:
Implementation of Item_sum_sum_distinct - SUM(DISTINCT) item,
which uses Unique to resolve duplicates
sql/item_sum.h:
New sum Item added - Item_sum_sum_distinct - for SUM(DISTINCT) function
sql/sql_class.h:
added walk() and reset() methods to Unique, used in Item_sum_sum_distinct.
sql/sql_sort.h:
declaration for reuse_freed_buff() to be able to use it in uniques.cc
sql/sql_yacc.yy:
parser extended to handle MIN(DISTICNT), MAX(DISTINCT), SUM(DISTINCT)
sql/uniques.cc:
Implementation for Unique::reset(), Unique::walk() as well as for merge_walk()
algorithm.
