4. View the Exhibit and examine the structure of the EMP table which is not partitioned and not an
indexorganized
table.
Evaluate the following SQL statement:
ALTER TABLE emp
DROP COLUMN first_name;
Which two statements are true regarding the above command? (Choose two.)
A. The FIRST_NAME column would be dropped provided it does not contain any data.
B. The FIRST_NAME column would be dropped provided at least one or more columns remain in the
table.
C. The FIRST_NAME column can be rolled back provided the SET UNUSED option is added to the above
SQL statement.
D. The FIRST_NAME column can be dropped even if it is part of a composite PRIMARY KEY provided
the CASCADE option is used.
Answer: BD
为什么D是正确的？请赐教
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