How to change the column type for Redshift.

update_column_type.sql

BEGIN;
LOCK table_name;
ALTER TABLE table_name ADD COLUMN column_new column_type;
UPDATE table_name SET column_new = column_name;
ALTER TABLE table_name DROP column_name;
ALTER TABLE table_name RENAME column_new TO column_name;
END;

-- varchar -> integer
--   UPDATE cpvbeacon_dev SET column_new = CAST (nullif(column_name, '') AS INTEGER);