Bug#44040 MySQL allows creating a MERGE table upon VIEWs but crashes when

        using it.
The crash was due to a null pointer present for select_lex while 
processing the view.
Adding a check while opening the view to see if its a child of a 
merge table fixed this problem.

mysql-test/r/merge.result:
  Updated result for the new test case.
mysql-test/t/merge.test:
  Added test case based on the bug description.
sql/sql_base.cc:
  Added a check to check if the view being opened is a child table of a
  merge table and return error if it is.

1 files changed, 10 insertions, 0 deletions

diff --git a/sql/sql_base.cc b/sql/sql_base.cc
index 0f0ee7c529e..0dc29f7e3c2 100644
--- a/sql/sql_base.cc
+++ b/sql/sql_base.cc
@@ -3844,6 +3844,16 @@ retry:
   if (share->is_view)
   {
     /*
+      If parent_l of the table_list is non null then a merge table
+      has this view as child table, which is not supported.
+    */
+    if (table_list->parent_l)
+    {
+      my_error(ER_WRONG_MRG_TABLE, MYF(0));
+      goto err;
+    }
+
+    /*
       This table is a view. Validate its metadata version: in particular,
       that it was a view when the statement was prepared.
     */