A fix for Bug#11901 "mysql_stmt_attr_set CURSOR_TYPE_READ_ONLY join in

subqry order by server crash": failing DBUG_ASSERT(curr_join == this)
when opening a cursor.
Ensure that for top-level join curr_join == join (always), 
and thus fix the failing assert.
curr_join is a hack to ensure that uncacheable subqueries can be
re-evaluated safely, and should be never different from main join
in case of top-level join.


sql/sql_select.cc:
  - utilize tmp_join only if we evaluate an uncacheable subquery.
sql/sql_select.h:
  - implement JOIN::is_top_level_join()
tests/mysql_client_test.c:
  A test case for Bug#11901 "mysql_stmt_attr_set CURSOR_TYPE_READ_ONLY
   join in subqry order by server crash"

1 files changed, 5 insertions, 0 deletions

diff --git a/sql/sql_select.h b/sql/sql_select.h
index c950444e1c6..3b9a3093682 100644
--- a/sql/sql_select.h
+++ b/sql/sql_select.h
@@ -366,6 +366,11 @@ class JOIN :public Sql_alloc
 	    !group_list);
   }
   bool change_result(select_result *result);
+  bool is_top_level_join() const
+  {
+    return (unit == &thd->lex->unit && (unit->fake_select_lex == 0 ||
+                                        select_lex == unit->fake_select_lex));
+  }
 };