Fix for bug #20732: Partial index and long sjis search with '>' fails sometimes

We miss some records sometimes using RANGE method if we have
partial key segments.
Example:
  Create table t1(a char(2), key(a(1)));
  insert into t1 values ('a'), ('xx');
  select a from t1 where a > 'x';
We call index_read() passing 'x' key and HA_READ_AFTER_KEY flag
in the handler::read_range_first() wich is wrong because we have
a partial key segment for the field and might miss records like 'xx'.

Fix: don't use open segments in such a case.

mysql-test/r/range.result

@@ -649,3 +649,13 @@ OR ((pk4 =1) AND (((pk1 IN ( 7, 2, 1 ))) OR (pk1 =522)) AND ((pk2 IN ( 0, 2635))
 pk1	pk2	pk3	pk4	filler
 2621	2635	1000015	0	filler
 drop table t1, t2;
+create table t1(a char(2), key(a(1)));
+insert into t1 values ('x'), ('xx');
+explain select a from t1 where a > 'x';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	range	a	a	2	NULL	2	Using where
+select a from t1 where a > 'x';
+a
+xx
+drop table t1;
+End of 4.1 tests

mysql-test/t/range.test

@@ -510,4 +510,14 @@ OR ((pk4 =1) AND (((pk1 IN ( 7, 2, 1 ))) OR (pk1 =522)) AND ((pk2 IN ( 0, 2635))
 ) AND (pk3 >=1000000);
 drop table t1, t2;
 
-# End of 4.1 tests
+#
+# Bug #20732: Partial index and long sjis search with '>' fails sometimes
+#
+
+create table t1(a char(2), key(a(1)));
+insert into t1 values ('x'), ('xx');
+explain select a from t1 where a > 'x';
+select a from t1 where a > 'x';
+drop table t1;
+
+--echo End of 4.1 tests

sql/opt_range.cc

@@ -885,6 +885,7 @@ int SQL_SELECT::test_quick_select(THD *thd, key_map keys_to_use,
 	key_parts->null_bit=	 key_part_info->null_bit;
         key_parts->image_type =
           (key_info->flags & HA_SPATIAL) ? Field::itMBR : Field::itRAW;
+        key_parts->flag=         key_part_info->key_part_flag;
       }
       param.real_keynr[param.keys++]=idx;
     }
@@ -1398,7 +1399,9 @@ get_mm_leaf(PARAM *param, COND *conf_func, Field *field, KEY_PART *key_part,
     }
     break;
   case Item_func::GT_FUNC:
-    if (field_is_equal_to_item(field,value))
+    /* Don't use open ranges for partial key_segments */
+    if (field_is_equal_to_item(field,value) &&
+        !(key_part->flag & HA_PART_KEY_SEG))
       tree->min_flag=NEAR_MIN;
     /* fall through */
   case Item_func::GE_FUNC:
@@ -2899,6 +2902,7 @@ QUICK_SELECT *get_quick_select_for_ref(THD *thd, TABLE *table, TABLE_REF *ref)
     key_part->length=  	    key_info->key_part[part].length;
     key_part->store_length= key_info->key_part[part].store_length;
     key_part->null_bit=     key_info->key_part[part].null_bit;
+    key_part->flag=         key_info->key_part[part].key_part_flag;
   }
   if (quick->ranges.push_back(range))
     goto err;

sql/opt_range.h

@@ -36,7 +36,7 @@
 
 typedef struct st_key_part {
   uint16           key,part, store_length, length;
-  uint8            null_bit;
+  uint8            null_bit, flag;
   Field            *field;
   Field::imagetype image_type;
 } KEY_PART;

sql/sql_select.cc

@@ -7337,7 +7337,7 @@ part_of_refkey(TABLE *table,Field *field)
 
     for (uint part=0 ; part < ref_parts ; part++,key_part++)
       if (field->eq(key_part->field) &&
-	  !(key_part->key_part_flag & HA_PART_KEY_SEG))
+	  !(key_part->key_part_flag & (HA_PART_KEY_SEG | HA_NULL_PART)))
 	return table->reginfo.join_tab->ref.items[part];
   }
   return (Item*) 0;

sql/table.cc

@@ -676,7 +676,7 @@ int openfrm(const char *name, const char *alias, uint db_stat, uint prgflag,
 	    as we need to test for NULL = NULL.
 	  */
 	  if (field->real_maybe_null())
-	    key_part->key_part_flag|= HA_PART_KEY_SEG;
+	    key_part->key_part_flag|= HA_NULL_PART;
 	}
 	else
 	{					// Error: shorten key