1 files changed, 6 insertions, 0 deletions
diff --git a/sql/sql_class.h b/sql/sql_class.h
index 5d3361d6c51..cdd655aec4c 100644
--- a/sql/sql_class.h
+++ b/sql/sql_class.h
@@ -1225,6 +1225,12 @@ public:
   ulonglong  limit_found_rows;
   ha_rows    cuted_fields,
              sent_row_count, examined_row_count;
+  /*
+    The set of those tables whose fields are referenced in all subqueries
+    of the query.
+    TODO: possibly this it is incorrect to have used tables in THD because
+    with more than one subquery, it is not clear what does the field mean.
+  */
   table_map  used_tables;
   USER_CONN *user_connect;
   CHARSET_INFO *db_charset;