Which three statements are true about the ALTER TABLE. . . .DROP COLUMN. . . . command?
A. A column can be dropped only if it does not contain any data.
B. A column can be dropped only if another column exists in the table.
C. A dropped column can be rolled back.
D. The column in a composite PRIMARY KEY with the CASCADE option can be dropped.
E. A parent key column in the table cannot be dropped.
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