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Examine the command that is used to create a table：  SQL> CREATE TABLE orders（oid NUMBER（6） PRIMARY KEY， odate DATE， ccode NUMBER（6）， oamt NUMBER（10，2）） TABLESPACE users；  Which two statements are true about the effect of the above command） （）
A:A CHECK constraint is created on the OID column.
B:A NOT NULL constraint is created on the OID column.
C:The ORDERS table is the only object created in the USERS tablespace.
D:The ORDERS table and a unique index are created in the USERS tablespace.
E:The ORDERS table is created in the USERS tablespace and a unique index is created on the OIDcolumn in the SYSTEM tablespace.

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出自：Oracle认证

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