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The EMPLOYEES table has these columns: Management wants to add a default value to the SALARY column. You plan to alter the table by using this SQL statement: What is true about your ALTER statement?（）
A:Column definitions cannot be altered to add DEFAULT values.
B:A change to the DEFAULT value affects only subsequent insertions to the table.
C:Column definitions cannot be altered at add DEFAULT values for columns with a NUMBER data type.
D:All the rows that have a NULL value for the SALARY column will be updated with the value 5000.

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出自：Oracle认证

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