Fixed bug mdev-5635.

After constant row substitution some field items become constant items.
The range analyzer should take into account this fact when looking for
ranges.

mysql-test/r/join.result

@@ -1538,3 +1538,14 @@ a
 3
 4
 DROP TABLE t1,t2;
+#
+# MDEV-5635: join of a const table with non-const tables
+# 
+CREATE TABLE t1 (a varchar(3) NOT NULL) ENGINE=MyISAM;
+INSERT INTO t1 VALUES ('foo');
+CREATE TABLE t2 (b varchar(3), c varchar(3), INDEX(b)) ENGINE=MyISAM;
+INSERT INTO t2 VALUES ('bar', 'bar'),( 'qux', 'qux');
+SELECT STRAIGHT_JOIN * FROM t1, t2 AS t2_1, t2 AS t2_2
+WHERE t2_2.c = t2_1.c AND t2_2.b = t2_1.b AND ( a IS NULL OR t2_1.c = a );
+a	b	c	b	c
+DROP TABLE t1,t2;

mysql-test/t/join.test

@@ -1185,3 +1185,18 @@ SELECT t1.a FROM t1 NATURAL STRAIGHT_JOIN t2 ORDER BY t1.a;
 SELECT t1.a FROM t1 NATURAL STRAIGHT_JOIN t2 ORDER BY t1.a;
 
 DROP TABLE t1,t2;
+
+--echo #
+--echo # MDEV-5635: join of a const table with non-const tables
+--echo # 
+
+CREATE TABLE t1 (a varchar(3) NOT NULL) ENGINE=MyISAM;
+INSERT INTO t1 VALUES ('foo');
+
+CREATE TABLE t2 (b varchar(3), c varchar(3), INDEX(b)) ENGINE=MyISAM;
+INSERT INTO t2 VALUES ('bar', 'bar'),( 'qux', 'qux');
+
+SELECT STRAIGHT_JOIN * FROM t1, t2 AS t2_1, t2 AS t2_2
+  WHERE t2_2.c = t2_1.c AND t2_2.b = t2_1.b AND ( a IS NULL OR t2_1.c = a );                  
+
+DROP TABLE t1,t2;

sql/opt_range.cc

@@ -7941,6 +7941,7 @@ static SEL_TREE *get_mm_tree(RANGE_OPT_PARAM *param,COND *cond)
       value= cond_func->arg_count > 1 ? cond_func->arguments()[1] : NULL;
       if (value && value->is_expensive())
         DBUG_RETURN(0);
+      if (!cond_func->arguments()[0]->real_item()->const_item())
         ftree= get_full_func_mm_tree(param, cond_func, field_item, value, inv);
     }
     /*
@@ -7966,6 +7967,7 @@ static SEL_TREE *get_mm_tree(RANGE_OPT_PARAM *param,COND *cond)
       value= cond_func->arguments()[0];
       if (value && value->is_expensive())
         DBUG_RETURN(0);
+      if (!cond_func->arguments()[1]->real_item()->const_item())
         ftree= get_full_func_mm_tree(param, cond_func, field_item, value, inv);
     }
   }