WL#926 "AVG(DISTINCT) and other distincts", part 2 (out of 3): clean up

Item_sum_count_distinct, and
deploy Unique for use with COUNT(DISTINCT) if there is no blob
column in the list of DISTINCT arguments.


mysql-test/r/count_distinct2.result:
  Test results fixed.
mysql-test/r/func_group.result:
  Updated.
mysql-test/r/sum_distinct.result:
  Updated.
mysql-test/t/func_group.test:
  Add a test for COUNT(DISTINCT) and true varchar and case-insensitive
  collation. The table in the test contains only two distinct values.
mysql-test/t/sum_distinct.test:
  Since now we support INSERT INTO t1 (a) SELECT a+1 FROM t1, shorten
  the test.
  Add a nominal test for AVG(DISTINCT)
sql/item_sum.cc:
  Implementation of cleaned up Item_sum_count_distinct.
  Fixed a bug with COUNT(DISTINCT) and new VARCHAR and collations.
  Fixed a bug wiht AVG(DISTINCT) and wrong number of output digits
  after decimal point.
sql/item_sum.h:
  Cleanup for Item_sum_count_distinct.
  Now if the list of distinct arguments doesn't contain a blob column,
  we always use Unique and merge-sort to find distinct values.
sql/sql_class.h:
  Added a short-cut to find number of elements in Unique if all elements fit
  into memory.

1 files changed, 7 insertions, 0 deletions

diff --git a/mysql-test/r/func_group.result b/mysql-test/r/func_group.result
index 46dba6cdfa9..81663cd9d66 100644
--- a/mysql-test/r/func_group.result
+++ b/mysql-test/r/func_group.result
@@ -881,3 +881,10 @@ SELECT MAX(id) FROM t1 WHERE id < 3 AND a=2 AND b=6;
 MAX(id)
 NULL
 DROP TABLE t1;
+CREATE TABLE t1 (a VARCHAR(400));
+INSERT INTO t1 (a) VALUES ("A"), ("a"), ("a "), ("a   "),
+("B"), ("b"), ("b "), ("b   ");
+SELECT COUNT(DISTINCT a) FROM t1;
+COUNT(DISTINCT a)
+2
+DROP TABLE t1;