Why is an outer "U" used?
Is there some reason an outer U is used to combine the four SELECTS for A,B,C,D rather than just select them directly? Is it just in case you'd like to refer to that union of 4 sets in the future?
1 answers ( 0 marked as helpful)
Hi Luke!
Thanks for reaching out.
It is used to define the whole subquery. It will work without using this alias but it is used for training subqueries.
Hope this helps.
Best,
Tsvetelin