45. Which two statements are true about sequences created in a single instance database? (Choose
two.)
A. The numbers generated by a sequence can be used only for one table.
B. DELETE <sequencename> would remove a sequence from the database.
C. CURRVAL is used to refer to the last sequence number that has been generated.
D. When the MAXVALUE limit for a sequence is reached, you can increase the MAXVALUE limit by using
the ALTER SEQUENCE statement.
E. When a database instance shuts down abnormally, the sequence numbers that have been cached but
not used would be available once again when the database instance is restarted.
Answer: CD
答案解析：
A不正确，因为一个序列生成的值可以用于多个表
B不正确，因为删除序列的语句为DROP SEQUENCE sequencename
C正确，对，CURRVAL是最后的那个值
D正确，对当最大值达到极限时，可以通过ALTER SEQUENCE修改序列来增加最大值
E不正确，因为如果内存非正常关闭，缓存的数会丢失。
如果建立序列时不指定CACHE和NOCACHE，默认值为20，
即一次性从序列里取20个数放入内存，如果内存崩溃，则这20个数就会丢失，再取值时从第21个数开始取值，CACHE设置的最小值为2。