Merge gkodinov@bk-internal.mysql.com:/home/bk/mysql-5.1-opt

into  rakia.gmz:/home/kgeorge/mysql/autopush/B16590-5.1-opt

mysql-test/r/order_by.result

@@ -926,3 +926,12 @@ NULL
 2
 3
 DROP TABLE t1,t2,t3,t4;
+CREATE TABLE t1 (a INT, b INT, PRIMARY KEY (a), UNIQUE KEY b (b));
+INSERT INTO t1 VALUES (1,1),(2,2);
+CREATE TABLE t2 (a INT, b INT, KEY a (a,b));
+INSERT INTO t2 VALUES (1,1),(1,2),(2,1),(2,2);
+EXPLAIN SELECT 1 FROM t1,t2 WHERE t1.b=2 AND t1.a=t2.a ORDER BY t2.b;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	const	PRIMARY,b	b	5	const	1	
+1	SIMPLE	t2	ref	a	a	5	const	2	Using where; Using index
+DROP TABLE t1,t2;

mysql-test/t/order_by.test

@@ -640,3 +640,16 @@ SELECT t2.b FROM t1 LEFT JOIN (t2, t3 LEFT JOIN t4 ON t3.a=t4.a)
 ON (t1.a=t2.a AND t1.b=t3.b) order by t2.b;
 
 DROP TABLE t1,t2,t3,t4;
+
+#
+# BUG#16590: Optimized does not do right "const" table pre-read
+#
+CREATE TABLE t1 (a INT, b INT, PRIMARY KEY (a), UNIQUE KEY b (b));
+INSERT INTO t1 VALUES (1,1),(2,2);
+
+CREATE TABLE t2 (a INT, b INT, KEY a (a,b));
+INSERT INTO t2 VALUES (1,1),(1,2),(2,1),(2,2);
+
+EXPLAIN SELECT 1 FROM t1,t2 WHERE t1.b=2 AND t1.a=t2.a ORDER BY t2.b;
+
+DROP TABLE t1,t2;

sql/sql_select.cc

@@ -7722,6 +7722,22 @@ static void update_const_equal_items(COND *cond, JOIN_TAB *tab)
         key_map possible_keys= field->key_start;
         possible_keys.intersect(field->table->keys_in_use_for_query);
         stat[0].const_keys.merge(possible_keys);
+
+        /*
+          For each field in the multiple equality (for which we know that it 
+          is a constant) we have to find its corresponding key part, and set 
+          that key part in const_key_parts.
+        */  
+        if (!possible_keys.is_clear_all())
+        {
+          TABLE *tab= field->table;
+          KEYUSE *use;
+          for (use= stat->keyuse; use && use->table == tab; use++)
+            if (possible_keys.is_set(use->key) && 
+                tab->key_info[use->key].key_part[use->keypart].field ==
+                field)
+              tab->const_key_parts[use->key]|= use->keypart_map;
+        }
       }
     }
   }