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.

3 files changed, 43 insertions, 0 deletions

diff --git a/mysql-test/r/merge.result b/mysql-test/r/merge.result
index d844abc1847..f53b328d14e 100644
--- a/mysql-test/r/merge.result
+++ b/mysql-test/r/merge.result
@@ -2115,4 +2115,16 @@ insert into m1 (col1) values (1);
 insert into m1 (col1) values (1);
 ERROR 23000: Duplicate entry '' for key '*UNKNOWN*'
 drop table m1, t1;
+CREATE TABLE t1 (
+col1 INT(10)
+) ENGINE=MyISAM  DEFAULT CHARSET=latin1;
+CREATE VIEW v1 as SELECT * FROM t1;
+CREATE TABLE m1 (
+col1 INT(10)
+)ENGINE=MRG_MyISAM DEFAULT CHARSET=latin1 INSERT_METHOD=LAST UNION=(v1);
+#Select should detect that the child table is a view and fail.
+SELECT * FROM m1;
+ERROR HY000: Unable to open underlying table which is differently defined or of non-MyISAM type or doesn't exist
+DROP VIEW v1;
+DROP TABLE m1, t1;
 End of 5.1 tests
diff --git a/mysql-test/t/merge.test b/mysql-test/t/merge.test
index f12187ea143..5315c91daa6 100644
--- a/mysql-test/t/merge.test
+++ b/mysql-test/t/merge.test
@@ -1514,4 +1514,25 @@ insert into m1 (col1) values (1);
 insert into m1 (col1) values (1);
 
 drop table m1, t1;
+
+#
+#Bug #44040   MySQL allows creating a MERGE table upon VIEWs but crashes 
+#when using it
+#
+
+CREATE TABLE t1 (
+        col1 INT(10)
+) ENGINE=MyISAM  DEFAULT CHARSET=latin1;
+
+CREATE VIEW v1 as SELECT * FROM t1;
+CREATE TABLE m1 (
+        col1 INT(10)
+)ENGINE=MRG_MyISAM DEFAULT CHARSET=latin1 INSERT_METHOD=LAST UNION=(v1);
+
+--echo #Select should detect that the child table is a view and fail.
+--error ER_WRONG_MRG_TABLE
+SELECT * FROM m1;
+
+DROP VIEW v1;
+DROP TABLE m1, t1;
 --echo End of 5.1 tests
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.
     */