CREATE TYPE droppabletype1 AS (a integer, b text);

CREATE TABlE testtable (droppablecol1 droppabletype1, undroppablecol1 int);

CREATE TYPE undroppabletype AS (a integer, b text);

ALTER TABLE testtable ADD COLUMN droppablecol2 droppabletype1;
ALTER TABLE testtable ADD COLUMN undroppablecol2 undroppabletype;

ALTER TABLE testtable ALTER COLUMN undroppablecol1 TYPE undroppabletype USING undroppablecol1::text::undroppabletype;
