1 files changed, 10 insertions, 0 deletions
diff --git a/sql/sql_window.cc b/sql/sql_window.cc
index 8fe2890d..e0c7cef1 100644
--- a/sql/sql_window.cc
+++ b/sql/sql_window.cc
@@ -429,6 +429,16 @@ ORDER *st_select_lex::find_common_window_func_partition_fields(THD *thd)
 #define CMP_GT_C       1    // Greater than and compatible
 #define CMP_GT         2    // Greater then
 
+
+/*
+  This function is used for sorting ORDER/PARTITION BY clauses of window
+  functions and so must implement an order relation on ORDER BY clauses"
+
+  It is called by a sorting function.
+  The function return's CMP_EQ (=0) if the values are identical.
+  If not equal, it returns a stable value < or > than 0.
+*/
+
 static
 int compare_order_elements(ORDER *ord1, int weight1,
                            ORDER *ord2, int weight2)