using NUM( over DUAL( is unnecessary and meaningless
We use DUAL() to assign numeric value to a text
but by using NUM( over Dual( we are only retaining the number returned by Match(), it should just be
Match(F1, 'Jan', 'Feb', 'Mar'))) as F3
Match() returns the position of the value found,
example if F1 was Jan it would return 1, if Mar then 3...