Properly handle `is null`

mysql-test/suite/oqgraph/isnull.result

+DROP TABLE IF EXISTS graph_base;
+DROP TABLE IF EXISTS graph;
+DROP TABLE IF EXISTS graph2;
+CREATE TABLE graph_base (
+from_id INT UNSIGNED NOT NULL,
+to_id INT UNSIGNED NOT NULL,
+PRIMARY KEY (from_id,to_id),
+INDEX (to_id)
+) ENGINE=MyISAM;
+CREATE TABLE graph (
+latch   VARCHAR(32) NULL,
+origid  BIGINT    UNSIGNED NULL,
+destid  BIGINT    UNSIGNED NULL,
+weight  DOUBLE    NULL,
+seq     BIGINT    UNSIGNED NULL,
+linkid  BIGINT    UNSIGNED NULL,
+KEY (latch, origid, destid) USING HASH,
+KEY (latch, destid, origid) USING HASH
+) ENGINE=OQGRAPH DATA_TABLE='graph_base' ORIGID='from_id', DESTID='to_id';
+INSERT INTO graph_base(from_id, to_id) VALUES (1,2), (2,1);
+INSERT INTO graph_base(from_id, to_id) VALUES (1,3), (3,1);
+INSERT INTO graph_base(from_id, to_id) VALUES (3,4), (4,3);
+INSERT INTO graph_base(from_id, to_id) VALUES (5,6), (6,5);
+select * from graph where latch is null;
+latch	origid	destid	weight	seq	linkid
+NULL	1	2	1	NULL	NULL
+NULL	2	1	1	NULL	NULL
+NULL	1	3	1	NULL	NULL
+NULL	3	1	1	NULL	NULL
+NULL	3	4	1	NULL	NULL
+NULL	4	3	1	NULL	NULL
+NULL	5	6	1	NULL	NULL
+NULL	6	5	1	NULL	NULL
+select * from graph where latch is null and origid=1;
+latch	origid	destid	weight	seq	linkid
+NULL	1	NULL	1	2	3
+NULL	1	NULL	1	1	2
+select * from graph where latch is null and destid=2;
+latch	origid	destid	weight	seq	linkid
+NULL	NULL	2	1	1	1
+DROP TABLE graph_base;
+DROP TABLE graph;

mysql-test/suite/oqgraph/isnull.test

@@ -31,6 +31,8 @@ INSERT INTO graph_base(from_id, to_id) VALUES (3,4), (4,3);
 INSERT INTO graph_base(from_id, to_id) VALUES (5,6), (6,5);
 
 select * from graph where latch is null;
+select * from graph where latch is null and origid=1;
+select * from graph where latch is null and destid=2;
 
 DROP TABLE graph_base;
 DROP TABLE graph;

storage/oqgraph/ha_oqgraph.cc

@@ -44,7 +44,7 @@
 #include "my_dbug.h"
 
 // Uncomment this for extra debug, but expect a performance hit in large queries
-#define VERBOSE_DEBUG
+//#define VERBOSE_DEBUG
 #ifdef VERBOSE_DEBUG
 #else
 #undef DBUG_PRINT
@@ -882,7 +882,10 @@ int ha_oqgraph::index_read_idx(byte * buf, uint index, const byte * key,
   // so we pass the string now.
   // In the future we should refactor parse_latch_string_to_legacy_int()
   // into oqgraph instead.
+  if (latchp)
     graph->retainLatchFieldValue(latchFieldValue.c_ptr_safe());
+  else
+    graph->retainLatchFieldValue(NULL);
     
   
   DBUG_PRINT( "oq-debug", ("index_read_idx ::>> search(latch:%s,%ld,%ld)", 
@@ -1095,7 +1098,7 @@ ha_rows ha_oqgraph::records_in_range(uint inx, key_range *min_key,
       min_key->flag != HA_READ_KEY_EXACT ||
       max_key->flag != HA_READ_AFTER_KEY)
   {
-    if (min_key->length == key->key_part[0].store_length)
+    if (min_key->length == key->key_part[0].store_length && !key->key_part[0].field->is_null()) /* ensure select * from x where latch is null is consistent with no latch */
     {
       // If latch is not null and equals 0, return # nodes