Shift/reduce conflict in window_spec clause: OVER (rows ...)

The window_spec clause in sql_yacc.yy has a shift/reduce conflict.

In a query like this:

SELECT .. COUNT(*) OVER (rows ...);

It's not clear what rows stands for. It can be ident in opt_window_ref:

SELECT ... COUNT(*) OVER (rows ORDER BY ...);

or the ROWS keyword in window_frame_units:

SELECT ... COUNT(*) OVER (ROWS BETWEEN 1 PRECEDING AND 1 FOLLOWING);

The conflict happens because ROWS is a non-reserved keyword in MariaDB.

Possible solutions:

• Make ROWS a reserved keyword, as in the SQL standard
• Or change the ident part in opt_window_ref to a new rule ident_window_ref which will not include ROWS.