Из Снежинки дата / время примеры :
select decode(extract ('dayofweek_iso',current_date()),
1, 'Monday',
2, 'Tuesday',
3, 'Wednesday',
4, 'Thursday',
5, 'Friday',
6, 'Saturday',
7, 'Sunday');
Альтернативно:
select decode(DAYNAME(CURRENT_DATE), 'Mon','Monday', 'Tues','Tuesday', ...);
select object_construct('Mon','Monday', 'Tues','Tuesday', ...)[DAYNAME(CURRENT_DATE)];