单项选择题

You need to change the definition of an existing table. The COMMERCIALS table needs its DESCRIPTION column changed to hold varying length characters up to 2000 bytes. The column can currently hold 1000 bytes per value. The table contains 20000 rows. Which statement is valid?（）

A. ALTER TABLE commercials MODIFY (description CHAR2(2000));
B. ALTER TABLE commercials CHANGE (description CHAR2(2000));
C. ALTER TABLE commercials CHANGE (description VARCHAR2 (2000));
D. ALTER TABLE commercials MODIFY (description VARCHAR2 (2000));
E. You cannot increase the size of a column if the table has rows.

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单项选择题What does the TRUNCATE statement do?（）

A. Removes the table
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C. Shortens the table to 10 rows
D. Removes all columns from a table
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单项选择题Which is an SQL*Plus command? （）

A. INSERT
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A. SELECT TO_CHAR(SYSDATE,'yyyy') FROM dual;
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A. All of the desired results
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A. Create groups of data
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