【多选题】
A A new column, COUNTRY, can be added to the DEPARTMENTS table after executing the command.
B Indexes created on the COUNTRY column exist until the DROP UNUSED COLUMNS command is executed.
C Unique key constraints defined on the COUNTRY column are removed.
D Synonyms existing on the DEPARTMENTS table would have to be re-created.
E Views created on the DEPARTMENTS table that include the COUNTRY column are automatically modified and remain valid.
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