Merge gkodinov@bk-internal.mysql.com:/home/bk/mysql-5.0-opt

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

mysql-test/r/distinct.result

@@ -530,7 +530,8 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 EXPLAIN SELECT DISTINCT a,b FROM t1 GROUP BY a,b;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	3	
-CREATE TABLE t2(a INT, b INT, c INT, d INT, PRIMARY KEY (a,b));
+CREATE TABLE t2(a INT, b INT NOT NULL, c INT NOT NULL, d INT, 
+PRIMARY KEY (a,b));
 INSERT INTO t2 VALUES (1,1,1,50), (1,2,3,40), (2,1,3,4);
 EXPLAIN SELECT DISTINCT a FROM t2;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
@@ -644,3 +645,26 @@ SELECT COUNT(*) FROM
 COUNT(*)
 2
 DROP TABLE t1, t2;
+CREATE TABLE t1 (a INT, UNIQUE (a));
+INSERT INTO t1 VALUES (4),(null),(2),(1),(null),(3);
+EXPLAIN SELECT DISTINCT a FROM t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	index	NULL	a	5	NULL	6	Using index
+SELECT DISTINCT a FROM t1;
+a
+NULL
+1
+2
+3
+4
+EXPLAIN SELECT a FROM t1 GROUP BY a;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	index	NULL	a	5	NULL	6	Using index
+SELECT a FROM t1 GROUP BY a;
+a
+NULL
+1
+2
+3
+4
+DROP TABLE t1;

mysql-test/t/distinct.test

@@ -364,7 +364,8 @@ EXPLAIN SELECT a FROM t1 GROUP BY a;
 EXPLAIN SELECT a,b FROM t1 GROUP BY a,b;
 EXPLAIN SELECT DISTINCT a,b FROM t1 GROUP BY a,b;
 
-CREATE TABLE t2(a INT, b INT, c INT, d INT, PRIMARY KEY (a,b));
+CREATE TABLE t2(a INT, b INT NOT NULL, c INT NOT NULL, d INT, 
+                PRIMARY KEY (a,b));
 INSERT INTO t2 VALUES (1,1,1,50), (1,2,3,40), (2,1,3,4);
 EXPLAIN SELECT DISTINCT a FROM t2;
 EXPLAIN SELECT DISTINCT a,a FROM t2;
@@ -525,3 +526,17 @@ SELECT COUNT(*) FROM
   (SELECT DISTINCT a FROM t2 WHERE a='oe' COLLATE latin1_german2_ci) dt;
 
 DROP TABLE t1, t2;
+
+#
+# Bug #25551: inconsistent behaviour in grouping NULL, depending on index type
+#
+CREATE TABLE t1 (a INT, UNIQUE (a));
+INSERT INTO t1 VALUES (4),(null),(2),(1),(null),(3);
+EXPLAIN SELECT DISTINCT a FROM t1;
+#result must have one row with NULL
+SELECT DISTINCT a FROM t1;
+EXPLAIN SELECT a FROM t1 GROUP BY a;
+#result must have one row with NULL
+SELECT a FROM t1 GROUP BY a;
+
+DROP TABLE t1;

sql/sql_select.cc

@@ -873,10 +873,11 @@ JOIN::optimize()
   }
   /*
      Check if we can optimize away GROUP BY/DISTINCT.
-     We can do that if there are no aggregate functions and the
+     We can do that if there are no aggregate functions, the
      fields in DISTINCT clause (if present) and/or columns in GROUP BY
      (if present) contain direct references to all key parts of
-     an unique index (in whatever order).
+     an unique index (in whatever order) and if the key parts of the
+     unique index cannot contain NULLs.
      Note that the unique keys for DISTINCT and GROUP BY should not
      be the same (as long as they are unique).
 
@@ -11918,7 +11919,8 @@ test_if_subkey(ORDER *order, TABLE *table, uint ref, uint ref_key_parts,
     of the table are referenced by a list : either the select list
     through find_field_in_item_list or GROUP BY list through
     find_field_in_order_list.
-    If the above holds then we can safely remove the GROUP BY/DISTINCT,
+    If the above holds and the key parts cannot contain NULLs then we 
+    can safely remove the GROUP BY/DISTINCT,
     as no result set can be more distinct than an unique key.
  
   RETURN VALUE
@@ -11943,7 +11945,8 @@ list_contains_unique_index(TABLE *table,
            key_part < key_part_end;
            key_part++)
       {
-        if (!find_func(key_part->field, data))
+        if (key_part->field->maybe_null() || 
+            !find_func(key_part->field, data))
           break;
       }
       if (key_part == key_part_end)