MDEV-18794 Assertion `!m_innodb' failed in ha_partition::cmp_ref upon SELECT from partitioned table

System versioning assertion fix. Since DROP SYSTEM VERSIONING does not
change list of dropped keys we should handle a special case.

Caused by MDEV-19751. This fix deprecates MDEV-17091.

mysql-test/suite/versioning/r/partition_innodb.result

@@ -65,3 +65,15 @@ partition by range columns (a, row_start) (
 partition p1 values less than (100, 100)
 );
 ERROR HY000: Transaction-precise system versioned tables do not support partitioning by ROW START or ROW END
+#
+# MDEV-18794 Assertion `!m_innodb' failed in ha_partition::cmp_ref upon SELECT from partitioned table
+#
+create or replace table t1 (pk int auto_increment, i int, c char(1), primary key (pk), key(i))
+engine=innodb with system versioning partition by key() partitions 2;
+insert into t1 (i, c) values (1, 'a'), (2, 'b'), (null, 'c'), (null, 'b');
+alter table t1 drop system versioning;
+replace into t1 select * from t1;
+select * from t1 where i > 0 or pk = 1000 limit 1;
+pk	i	c
+1	1	a
+drop table t1;

mysql-test/suite/versioning/t/partition_innodb.test

@@ -78,4 +78,15 @@ partition by range columns (a, row_start) (
   partition p1 values less than (100, 100)
 );
 
+--echo #
+--echo # MDEV-18794 Assertion `!m_innodb' failed in ha_partition::cmp_ref upon SELECT from partitioned table
+--echo #
+create or replace table t1 (pk int auto_increment, i int, c char(1), primary key (pk), key(i))
+engine=innodb with system versioning partition by key() partitions 2;
+insert into t1 (i, c) values (1, 'a'), (2, 'b'), (null, 'c'), (null, 'b');
+alter table t1 drop system versioning;
+replace into t1 select * from t1;
+select * from t1 where i > 0 or pk = 1000 limit 1;
+drop table t1;
+
 --source suite/versioning/common_finish.inc

sql/sql_partition.cc

@@ -5986,26 +5986,35 @@ the generated partition syntax in a correct manner.
         }
       }
       /*
-        Prohibit inplace when partitioned by primary key and the primary key is dropped.
+        Prohibit inplace when partitioned by primary key and the primary key is changed.
       */
       if (!*partition_changed &&
           tab_part_info->part_field_array &&
           !tab_part_info->part_field_list.elements &&
           table->s->primary_key != MAX_KEY)
       {
-        KEY *primary_key= table->key_info + table->s->primary_key;
-        List_iterator_fast<Alter_drop> drop_it(alter_info->drop_list);
-        const char *primary_name= primary_key->name.str;
-        const Alter_drop *drop;
-        drop_it.rewind();
-        while ((drop= drop_it++))
+
+        if (alter_info->flags & (ALTER_DROP_SYSTEM_VERSIONING |
+                                 ALTER_ADD_SYSTEM_VERSIONING))
         {
-          if (drop->type == Alter_drop::KEY &&
-              0 == my_strcasecmp(system_charset_info, primary_name, drop->name))
-            break;
+          *partition_changed= true;
+        }
+        else
+        {
+          KEY *primary_key= table->key_info + table->s->primary_key;
+          List_iterator_fast<Alter_drop> drop_it(alter_info->drop_list);
+          const char *primary_name= primary_key->name.str;
+          const Alter_drop *drop;
+          drop_it.rewind();
+          while ((drop= drop_it++))
+          {
+            if (drop->type == Alter_drop::KEY &&
+                0 == my_strcasecmp(system_charset_info, primary_name, drop->name))
+              break;
+          }
+          if (drop)
+            *partition_changed= TRUE;
         }
-        if (drop)
-          *partition_changed= TRUE;
       }
     }
     if (thd->work_part_info)
@@ -6039,23 +6048,6 @@ the generated partition syntax in a correct manner.
         }
       }
 
-      // In case of PARTITION BY KEY(), check if primary key has changed
-      // System versioning also implicitly adds/removes primary key parts
-      if (alter_info->partition_flags == 0 && part_info->list_of_part_fields
-          && part_info->part_field_list.elements == 0)
-      {
-        if (alter_info->flags & (ALTER_DROP_SYSTEM_VERSIONING |
-                                 ALTER_ADD_SYSTEM_VERSIONING))
-          *partition_changed= true;
-
-        List_iterator<Key> it(alter_info->key_list);
-        Key *key;
-        while((key= it++) && !*partition_changed)
-        {
-          if (key->type == Key::PRIMARY)
-            *partition_changed= true;
-        }
-      }
       /*
         Set up partition default_engine_type either from the create_info
         or from the previus table