-- UNPIVOT [ { INCLUDE | EXCLUDE } NULLS ] (
--     { single_value_column_unpivot | multi_value_column_unpivot }
-- ) [[AS] alias]

-- single_value_column_unpivot:
--     values_column
--     FOR name_column
--     IN (unpivot_column [[AS] alias] [, ...])

-- multi_value_column_unpivot:
--     (values_column [, ...])
--     FOR name_column
--     IN ((unpivot_column [, ...]) [[AS] alias] [, ...])


-- column names are used as unpivot columns
SELECT * FROM sales_quarterly
    UNPIVOT (
        sales FOR quarter IN (q1, q2, q3, q4)
    );

-- NULL values are excluded by default, they can be included
-- unpivot columns can be alias
-- unpivot result can be referenced via its alias
SELECT up.* FROM sales_quarterly
    UNPIVOT INCLUDE NULLS (
        sales FOR quarter IN (q1 AS Q1, q2 AS Q2, q3 AS Q3, q4 AS Q4)
    ) AS up;

-- multiple value columns can be unpivoted per row
SELECT * FROM sales_quarterly
    UNPIVOT EXCLUDE NULLS (
        (first_quarter, second_quarter)
        FOR half_of_the_year IN (
            (q1, q2) AS H1,
            (q3, q4) AS H2
        )
    );