SQL function in presto CROSS JOIN statement

Question

Trying to understand the presto CROSS JOIN and UNNEST statements from the docs here , there is a code snippet that I don't understand:

SELECT student, score
FROM tests
CROSS JOIN UNNEST(scores) AS t (score);

I don't understand the lowercase t -- is it a function? What does it do? In my own tables, the query stops working when I remove the t and the parentheses, but I can't understand why.

Answer 1

t is an alias, not a function. UNNEST(scores) AS t provides a virtual table, aliased t .