MDEV-5606: range optimizer: "x < y" is sargable, while "y > x" is not

Port to mariadb-1.0 the following fix from mysql-5.6:

  Revision ID: jorgen.loland@oracle.com-20120314131055-ml54x9deueqfsff4
  BUG#13701206: WHERE A>=B DOES NOT GIVE SAME EXECUTION PLAN
                AS WHERE B<=A (RANGE OPTIMIZER)
 
that fix didn't have a public testcase, so I created one.

mysql-test/r/range.result

@@ -2046,3 +2046,34 @@ f1	f2	f3	f4
 10	0	0	0
 DROP TABLE t1;
 DROP VIEW v3;
+#
+#  MDEV-5606: range optimizer: "x < y" is sargable, while "y > x" is not
+#
+create table t1(a int);
+insert into t1 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+create table t2(a int);
+insert into t2 select A.a + B.a* 10 + C.a * 100 from t1 A, t1 B, t1 C;
+alter table t2 add key(a);
+# Should have "range checked for each table" for second table:
+explain select * from t1, t2 where t2.a < t1.a;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	10	
+1	SIMPLE	t2	ALL	a	NULL	NULL	NULL	1000	Range checked for each record (index map: 0x1)
+# Should have "range checked for each table" for second table:
+explain select * from t1, t2 where t1.a > t2.a;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	10	
+1	SIMPLE	t2	ALL	a	NULL	NULL	NULL	1000	Range checked for each record (index map: 0x1)
+create table t3 (a int primary key, b int);
+insert into t3 select a,a from t1;
+# The second table should use 'range':
+explain select * from t3, t2 where t2.a < t3.b  and t3.a=1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t3	const	PRIMARY	PRIMARY	4	const	1	
+1	SIMPLE	t2	range	a	a	5	NULL	1	Using where; Using index
+# The second table should use 'range':
+explain select * from t3, t2 where t3.b > t2.a   and t3.a=1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t3	const	PRIMARY	PRIMARY	4	const	1	
+1	SIMPLE	t2	range	a	a	5	NULL	1	Using where; Using index
+drop table t1,t2,t3;

mysql-test/r/range_mrr_icp.result

@@ -2048,4 +2048,35 @@ f1	f2	f3	f4
 10	0	0	0
 DROP TABLE t1;
 DROP VIEW v3;
+#
+#  MDEV-5606: range optimizer: "x < y" is sargable, while "y > x" is not
+#
+create table t1(a int);
+insert into t1 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+create table t2(a int);
+insert into t2 select A.a + B.a* 10 + C.a * 100 from t1 A, t1 B, t1 C;
+alter table t2 add key(a);
+# Should have "range checked for each table" for second table:
+explain select * from t1, t2 where t2.a < t1.a;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	10	
+1	SIMPLE	t2	ALL	a	NULL	NULL	NULL	1000	Range checked for each record (index map: 0x1)
+# Should have "range checked for each table" for second table:
+explain select * from t1, t2 where t1.a > t2.a;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	10	
+1	SIMPLE	t2	ALL	a	NULL	NULL	NULL	1000	Range checked for each record (index map: 0x1)
+create table t3 (a int primary key, b int);
+insert into t3 select a,a from t1;
+# The second table should use 'range':
+explain select * from t3, t2 where t2.a < t3.b  and t3.a=1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t3	const	PRIMARY	PRIMARY	4	const	1	
+1	SIMPLE	t2	range	a	a	5	NULL	1	Using where; Using index
+# The second table should use 'range':
+explain select * from t3, t2 where t3.b > t2.a   and t3.a=1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t3	const	PRIMARY	PRIMARY	4	const	1	
+1	SIMPLE	t2	range	a	a	5	NULL	1	Using where; Using index
+drop table t1,t2,t3;
 set optimizer_switch=@mrr_icp_extra_tmp;

mysql-test/t/range.test

@@ -1639,3 +1639,24 @@ SELECT * FROM v3;
 DROP TABLE t1;
 DROP VIEW v3;
 
+--echo #
+--echo #  MDEV-5606: range optimizer: "x < y" is sargable, while "y > x" is not
+--echo #
+create table t1(a int);
+insert into t1 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+create table t2(a int);
+insert into t2 select A.a + B.a* 10 + C.a * 100 from t1 A, t1 B, t1 C;
+alter table t2 add key(a);
+--echo # Should have "range checked for each table" for second table:
+explain select * from t1, t2 where t2.a < t1.a;
+--echo # Should have "range checked for each table" for second table:
+explain select * from t1, t2 where t1.a > t2.a;
+
+create table t3 (a int primary key, b int);
+insert into t3 select a,a from t1;
+--echo # The second table should use 'range':
+explain select * from t3, t2 where t2.a < t3.b  and t3.a=1;
+--echo # The second table should use 'range':
+explain select * from t3, t2 where t3.b > t2.a   and t3.a=1;
+drop table t1,t2,t3;
+

sql/opt_range.cc

@@ -7684,7 +7684,8 @@ static SEL_TREE *get_func_mm_tree(RANGE_OPT_PARAM *param, Item_func *cond_func,
       param       PARAM from SQL_SELECT::test_quick_select
       cond_func   item for the predicate
       field_item  field in the predicate
-      value       constant in the predicate
+      value       constant in the predicate (or a field already read from 
+                  a table in the case of dynamic range access)
                   (for BETWEEN it contains the number of the field argument,
                    for IN it's always 0) 
       inv         TRUE <> NOT cond_func is considered
@@ -7953,25 +7954,42 @@ static SEL_TREE *get_mm_tree(RANGE_OPT_PARAM *param,COND *cond)
     DBUG_RETURN(ftree);
   }
   default:
+
+    DBUG_ASSERT (!ftree);
     if (cond_func->arguments()[0]->real_item()->type() == Item::FIELD_ITEM)
     {
       field_item= (Item_field*) (cond_func->arguments()[0]->real_item());
-      value= cond_func->arg_count > 1 ? cond_func->arguments()[1] : 0;
+      value= cond_func->arg_count > 1 ? cond_func->arguments()[1] : NULL;
+      if (value && value->is_expensive())
+        DBUG_RETURN(0);
+      ftree= get_full_func_mm_tree(param, cond_func, field_item, value, inv);
     }
-    else if (cond_func->have_rev_func() &&
-             cond_func->arguments()[1]->real_item()->type() ==
-                                                            Item::FIELD_ITEM)
+    /*
+      Even if get_full_func_mm_tree() was executed above and did not
+      return a range predicate it may still be possible to create one
+      by reversing the order of the operands. Note that this only
+      applies to predicates where both operands are fields. Example: A
+      query of the form
+
+         WHERE t1.a OP t2.b
+
+      In this case, arguments()[0] == t1.a and arguments()[1] == t2.b.
+      When creating range predicates for t2, get_full_func_mm_tree()
+      above will return NULL because 'field' belongs to t1 and only
+      predicates that applies to t2 are of interest. In this case a
+      call to get_full_func_mm_tree() with reversed operands (see
+      below) may succeed.
+    */
+    if (!ftree && cond_func->have_rev_func() &&
+        cond_func->arguments()[1]->real_item()->type() == Item::FIELD_ITEM)
     {
       field_item= (Item_field*) (cond_func->arguments()[1]->real_item());
       value= cond_func->arguments()[0];
-    }
-    else
-      DBUG_RETURN(0);
       if (value && value->is_expensive())
         DBUG_RETURN(0);
-
       ftree= get_full_func_mm_tree(param, cond_func, field_item, value, inv);
     }
+  }
 
   DBUG_RETURN(ftree);
 }