MDEV-17387 MariaDB Server giving wrong error while executing select query from procedure

Changing the way how a cursor is opened to fetch its structure only,
e.g. for a cursor FOR loop record variable.

The old methods with setting thd->lex->limit_rows_examined to an Item_uint(0)
was not reliable and could push these messages into diagnostics area:

  The query examined at least 1 rows, which exceeds LIMIT ROWS EXAMINED (0)

The new method should be more reliable, as it completely prevents the call
of do_select() in JOIN::exec_inner() during the cursor structure discovery,
so the execution of the cursor SELECT query returns immediately after the
preparation step (when the result row structure becomes known),
without even entering the code that fetches the result rows.

1 files changed, 5 insertions, 0 deletions

diff --git a/sql/sql_cursor.cc b/sql/sql_cursor.cc
index 2a200d279b5..4f3b15c3254 100644
--- a/sql/sql_cursor.cc
+++ b/sql/sql_cursor.cc
@@ -92,6 +92,11 @@ public:
     if (materialized_cursor)
       materialized_cursor->on_table_fill_finished();
   }
+
+  bool view_structure_only() const
+  {
+    return result->view_structure_only();
+  }
 };