Fixed bug mdev-6705.

After constant row substitution the WHERE condition may be simplified and its multiple equality
may be changed. In this case the references to these multiple equalities from the COND_EQUAL
objects associated with ON expressions must be updated.
Also we have to take into account that this simplification may lead to equalities of the form
field=const that are mutually exclusive with some of the equalities in ON expressions. 

mysql-test/r/join_outer.result

@@ -1920,4 +1920,27 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 Warnings:
 Note	1003	select `test`.`t1`.`i1` AS `i1`,`test`.`t2`.`i2` AS `i2`,`test`.`t3`.`i3` AS `i3`,`test`.`t3`.`d3` AS `d3` from `test`.`t1` left join (`test`.`t2` join `test`.`t3`) on(((`test`.`t2`.`i2` = `test`.`t1`.`i1`) and (`test`.`t3`.`i3` = `test`.`t1`.`i1`))) where ((`test`.`t3`.`d3` = 0) or isnull(`test`.`t3`.`d3`))
 DROP TABLE t1,t2,t3;
+#
+# Bug mdev-6705: wrong on expression after constant row substitution 
+#                that triggers a simplification of WHERE condition
+#
+CREATE TABLE t1 (a int, b int) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (10,8);
+CREATE TABLE t2 (c int) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (8),(9);
+CREATE TABLE t3 (d int) ENGINE=MyISAM;
+INSERT INTO t3 VALUES (3),(8);
+EXPLAIN EXTENDED
+SELECT * FROM t1 INNER JOIN t2 ON c = b LEFT JOIN t3 ON d = a
+WHERE b IN (1,2,3) OR b = d;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	system	NULL	NULL	NULL	NULL	1	100.00	
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
+1	SIMPLE	t3	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
+Warnings:
+Note	1003	select 10 AS `a`,8 AS `b`,`test`.`t2`.`c` AS `c`,`test`.`t3`.`d` AS `d` from `test`.`t1` join `test`.`t2` left join `test`.`t3` on((`test`.`t3`.`d` = 10)) where ((`test`.`t2`.`c` = 8) and (`test`.`t3`.`d` = 8))
+SELECT * FROM t1 INNER JOIN t2 ON c = b LEFT JOIN t3 ON d = a
+WHERE b IN (1,2,3) OR b = d;
+a	b	c	d
+DROP TABLE t1,t2,t3;
 SET optimizer_switch=@save_optimizer_switch;

mysql-test/r/join_outer_jcl6.result

@@ -1931,6 +1931,29 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 Warnings:
 Note	1003	select `test`.`t1`.`i1` AS `i1`,`test`.`t2`.`i2` AS `i2`,`test`.`t3`.`i3` AS `i3`,`test`.`t3`.`d3` AS `d3` from `test`.`t1` left join (`test`.`t2` join `test`.`t3`) on(((`test`.`t2`.`i2` = `test`.`t1`.`i1`) and (`test`.`t3`.`i3` = `test`.`t1`.`i1`))) where ((`test`.`t3`.`d3` = 0) or isnull(`test`.`t3`.`d3`))
 DROP TABLE t1,t2,t3;
+#
+# Bug mdev-6705: wrong on expression after constant row substitution 
+#                that triggers a simplification of WHERE condition
+#
+CREATE TABLE t1 (a int, b int) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (10,8);
+CREATE TABLE t2 (c int) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (8),(9);
+CREATE TABLE t3 (d int) ENGINE=MyISAM;
+INSERT INTO t3 VALUES (3),(8);
+EXPLAIN EXTENDED
+SELECT * FROM t1 INNER JOIN t2 ON c = b LEFT JOIN t3 ON d = a
+WHERE b IN (1,2,3) OR b = d;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	system	NULL	NULL	NULL	NULL	1	100.00	
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
+1	SIMPLE	t3	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where; Using join buffer (flat, BNL join)
+Warnings:
+Note	1003	select 10 AS `a`,8 AS `b`,`test`.`t2`.`c` AS `c`,`test`.`t3`.`d` AS `d` from `test`.`t1` join `test`.`t2` left join `test`.`t3` on((`test`.`t3`.`d` = 10)) where ((`test`.`t2`.`c` = 8) and (`test`.`t3`.`d` = 8))
+SELECT * FROM t1 INNER JOIN t2 ON c = b LEFT JOIN t3 ON d = a
+WHERE b IN (1,2,3) OR b = d;
+a	b	c	d
+DROP TABLE t1,t2,t3;
 SET optimizer_switch=@save_optimizer_switch;
 set join_cache_level=default;
 show variables like 'join_cache_level';

mysql-test/t/join_outer.test

@@ -1463,4 +1463,28 @@ SELECT * FROM t1 LEFT JOIN t2 LEFT JOIN t3 ON i2 = i3 ON i1 = i3
 
 DROP TABLE t1,t2,t3;
 
+--echo #
+--echo # Bug mdev-6705: wrong on expression after constant row substitution 
+--echo #                that triggers a simplification of WHERE condition
+--echo #
+
+CREATE TABLE t1 (a int, b int) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (10,8);
+
+CREATE TABLE t2 (c int) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (8),(9);
+
+CREATE TABLE t3 (d int) ENGINE=MyISAM;
+INSERT INTO t3 VALUES (3),(8);
+
+EXPLAIN EXTENDED
+SELECT * FROM t1 INNER JOIN t2 ON c = b LEFT JOIN t3 ON d = a
+  WHERE b IN (1,2,3) OR b = d;
+
+SELECT * FROM t1 INNER JOIN t2 ON c = b LEFT JOIN t3 ON d = a
+  WHERE b IN (1,2,3) OR b = d;
+
+DROP TABLE t1,t2,t3;
+
+
 SET optimizer_switch=@save_optimizer_switch;

sql/sql_select.cc

@@ -3530,6 +3530,7 @@ make_join_statistics(JOIN *join, List<TABLE_LIST> &tables_list,
   join->impossible_where= false;
   if (conds && const_count)
   { 
+    COND_EQUAL *orig_cond_equal = join->cond_equal;
     conds->update_used_tables();
     conds= remove_eq_conds(join->thd, conds, &join->cond_value);
     if (conds && conds->type() == Item::COND_ITEM &&
@@ -3557,6 +3558,20 @@ make_join_statistics(JOIN *join, List<TABLE_LIST> &tables_list,
         join->cond_equal->current_level.push_back((Item_equal*) conds);
       }
     }
+
+    if (orig_cond_equal != join->cond_equal)
+    {
+      /*
+        If join->cond_equal has changed all references to it from COND_EQUAL
+        objects associated with ON expressions must be updated.
+      */
+      for (JOIN_TAB **pos=stat_vector+const_count ; (s= *pos) ; pos++) 
+      {
+        if (*s->on_expr_ref && s->cond_equal &&
+	    s->cond_equal->upper_levels == orig_cond_equal)
+          s->cond_equal->upper_levels= join->cond_equal;
+      }
+    }
   }
 
   /* Calc how many (possible) matched records in each table */
@@ -11999,9 +12014,17 @@ Item *eliminate_item_equal(COND *cond, COND_EQUAL *upper_levels,
     if (upper)
     {
       TABLE_LIST *native_sjm= embedding_sjm(item_equal->context_field);
-      if (item_const && upper->get_const())
+      Item *upper_const= upper->get_const();
+      if (item_const && upper_const)
       {
-        /* Upper item also has "field_item=const". Don't produce equality here */
+        /* 
+          Upper item also has "field_item=const".
+          Don't produce equality if const is equal to item_const.
+        */
+        Item_func_eq *func= new Item_func_eq(item_const, upper_const);
+        func->set_cmp_func();
+        func->quick_fix_field();
+        if (func->val_int())
           item= 0;
       }
       else