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Examine the data in the EMPLOYEES table. On the EMPLOYEES table, EMPLOYEE_ID is the primary key. MGR_ID is the ID of managers and refers to the EMPLOYEE_ID. The JOB_ID column is a NOT NULL column. Evaluate this DELETE statement: Why does the DELETE statement fail when you execute it?（）
A:There is no row with dept_id 90 in the EMPLOYEES table.
B:You cannot delete the JOB_ID column because it is a NOT NULL column.
C:You cannot specify column names in the DELETE clause of the DELETE statement.
D:You cannot delete the EMPLOYEE_ID column because it is the primary key of the table.

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出自：Oracle认证

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