Bug#38005 Partitions: error with insert select.

MyISAM blocks index usage for bulk insert into zero-records tables.
See ha_myisam::start_bulk_insert() lines from
...
    if (file->state->records == 0 ...
...

That causes problems for partition engine when some partitions have records some not
as the engine uses same access method for all partitions.

Now partition engine doesn't call index_first/index_last
for empty tables.

per-file comments:
  mysql-test/r/partition.result
        Bug#38005 Partitions: error with insert select.
        test result

  mysql-test/t/partition.test
        Bug#38005 Partitions: error with insert select.
        test case

  sql/ha_partition.cc
        Bug#38005 Partitions: error with insert select.
        ha_engine::index_first and
        ha_engine::index_last not called for empty tables.

1 files changed, 33 insertions, 0 deletions

diff --git a/sql/ha_partition.cc b/sql/ha_partition.cc
index ea42858356d..14e321218ca 100644
--- a/sql/ha_partition.cc
+++ b/sql/ha_partition.cc
@@ -4290,6 +4290,17 @@ int ha_partition::handle_unordered_scan_next_partition(uchar * buf)
       break;
     case partition_index_first:
       DBUG_PRINT("info", ("index_first on partition %d", i));
+      /* MyISAM engine can fail if we call index_first() when indexes disabled */
+      /* that happens if the table is empty. */
+      /* Here we use file->stats.records instead of file->records() because */
+      /* file->records() is supposed to return an EXACT count, and it can be   */
+      /* possibly slow. We don't need an exact number, an approximate one- from*/
+      /* the last ::info() call - is sufficient. */
+      if (file->stats.records == 0)
+      {
+        error= HA_ERR_END_OF_FILE;
+        break;
+      }
       error= file->index_first(buf);
       break;
     case partition_index_first_unordered:
@@ -4377,10 +4388,32 @@ int ha_partition::handle_ordered_index_scan(uchar *buf, bool reverse_order)
                                   m_start_key.flag);
       break;
     case partition_index_first:
+      /* MyISAM engine can fail if we call index_first() when indexes disabled */
+      /* that happens if the table is empty. */
+      /* Here we use file->stats.records instead of file->records() because */
+      /* file->records() is supposed to return an EXACT count, and it can be   */
+      /* possibly slow. We don't need an exact number, an approximate one- from*/
+      /* the last ::info() call - is sufficient. */
+      if (file->stats.records == 0)
+      {
+        error= HA_ERR_END_OF_FILE;
+        break;
+      }
       error= file->index_first(rec_buf_ptr);
       reverse_order= FALSE;
       break;
     case partition_index_last:
+      /* MyISAM engine can fail if we call index_last() when indexes disabled */
+      /* that happens if the table is empty. */
+      /* Here we use file->stats.records instead of file->records() because */
+      /* file->records() is supposed to return an EXACT count, and it can be   */
+      /* possibly slow. We don't need an exact number, an approximate one- from*/
+      /* the last ::info() call - is sufficient. */
+      if (file->stats.records == 0)
+      {
+        error= HA_ERR_END_OF_FILE;
+        break;
+      }
       error= file->index_last(rec_buf_ptr);
       reverse_order= TRUE;
       break;