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You need to replicate a table from a master to a slave. The master and slave copies of the table will have different number of columns. Which two conditions must be true?（）
A:Each extra column in the copy with more columns must not have a default value
B:Columns that are common to both versions of the table must be defined in the same order on the master and the slave
C:The slave database cannot have more columns than the master. Only the master database can have more columns
D:Columns that are common to both versions of the table must come first in the table definition, before any additional columns are additional columns are defined on either server
E:The master database cannot have more columns than the slave. Only the slave deatbase can have more columns

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出自：Oracle认证

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