merging.

mysql-test/t/partition_innodb.test

@@ -577,6 +577,19 @@ connection default;
 SELECT * FROM t1;
 COMMIT;
 DROP TABLE t1;
+
+#
+# Bug #55146    Assertion `m_part_spec.start_part == m_part_spec.end_part' in index_read_idx_map
+#
+
+CREATE TABLE t1 (i1 int NOT NULL primary key, f1 int) ENGINE = InnoDB
+    PARTITION BY HASH(i1) PARTITIONS 2;
+
+INSERT INTO t1 VALUES (1,1), (2,2);
+
+SELECT * FROM t1 WHERE i1 = ( SELECT i1 FROM t1 WHERE f1=0 LIMIT 1 );
+DROP TABLE t1;
+
 --enable_parsing
 
 --echo #

sql/ha_partition.cc

@@ -4382,8 +4382,12 @@ int ha_partition::index_read_idx_map(uchar *buf, uint index,
 
     get_partition_set(table, buf, index, &m_start_key, &m_part_spec);
 
-    /* How can it be more than one partition with the current use? */
-    DBUG_ASSERT(m_part_spec.start_part == m_part_spec.end_part);
+    /* 
+      We have either found exactly 1 partition
+      (in which case start_part == end_part)
+      or no matching partitions (start_part > end_part)
+    */
+    DBUG_ASSERT(m_part_spec.start_part >= m_part_spec.end_part);
 
     for (part= m_part_spec.start_part; part <= m_part_spec.end_part; part++)
     {