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【单项选择题】

If a unique constraint is defined on column COL1 of table TAB1, what are the characteristics of COL1?（）

A、A.COL1 will accept NULL values and can be referenced in another table's foreign key specification.

B、B.COL1 will not accept NULL values and cannot be referenced in another tables foreign key specification.

C、C.COL1 will not accept NULL values and can be referenced in another tables foreign key specification.

D、D.COL1 will accept NULL values and cannot be referenced in another tables foreign key specification.

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更多“If a unique constraint is defined on column COL1 of table TAB1, what are the characteristics of COL1?（）”相关的问题
第1题
[] 在数据表设计时，UNIQUE与PRIMAR YKEY两者的区别是（）

A、A.UNIQUE要求数据表中至少存在一行数据，必须在建表后创建，而PRIMARY KEY无该限制  B、B.UNIQUE允许空值存在，而PRIMARYKEY不允许  C、C.创建UNIQUE后，该数据行允许被修改，而PRIMARYKEY则不允许  D、D.UNIQUE列不能创建外键，而PRIMARYKEY可以创建外键  

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第2题
[单选题] Which of the following is true of an index used to support a UNIQUE constraint?（）

A、It must have the UNIQUE attribute.  B、It cannot be created explicitly by the user.  C、It must have the UNIQUE and CLUSTER attributes.  D、It must have the UNIQUE WHERE NOT NULL attribute.  

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第3题
[多选题] Which two statements are true about constraints? （）

A、The UNIQUE constraint does not permit a null value for the column.  B、A UNIQUE index gets created for columns with PRIMARY KEY and UNIQUE constraints.  C、The PRIMARY KEY and FOREIGN KEY constraints create a UNIQUE index.  D、The NOT NULL constraint ensures that null values are not permitted for the column.  

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第4题
[多选题] Which two statements are true about constraints? （）

A、The UNIQUE constraint does not permit a null value for the column.  B、A UNIQUE index gets created for columns with PRIMARY KEY and UNIQUE constraints.  C、The PRIMARY KEY and FOREIGN KEY constraints create a UNIQUE index.  D、The NOT NULL constraint ensures that null values are not permitted for the column.  

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第5题
[多选题] Which two statements are true about constraints? （）

A、The UNIQUE constraint does not permit a null value for the column.  B、A UNIQUE index gets created for columns with PRIMARY KEY and UNIQUE constraints.  C、The PRIMARY KEY and FOREIGN KEY constraints create a UNIQUE index.  D、The NOT NULL constraint ensures that null values are not permitted for the column.  

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第6题
[多选题] Which two statements are true about constraints? （）

A、The UNIQUE constraint does not permit a null value for the column.  B、A UNIQUE index gets created for columns with PRIMARY KEY and UNIQUE constraints.  C、The PRIMARY KEY and FOREIGN KEY constraints create a UNIQUE index.  D、The NOT NULL constraint ensures that null values are not permitted for the column.  

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第7题
[单选题] Table TAB1 was created using the following statement: CREATE TABLE tab1 (c1 INT, c2 INT, c3 INT, c4 INT, c5 INT); If column C1 is unique and queries typically access columns C1 and C2 together, which statement(s) will create index(es) that will provide optimal query performance? （）

A、 CREATE UNIQUE INDEX xtab1 ON tab1 (c1) include (c2)  B、 CREATE UNIQUE INDEX xtab1 ON tab1 (c1);  CREATE INDEX xtab2 ON tab1 (c3) INCLUDE (c2)   C、 CREATE UNIQUE INDEX xtab1 ON tab1 (c2, c1)  D、 CREATE UNIQUE INDEX xtab1 ON tab1 (c2) INCLUDE (c1）  

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第8题
[单选题] Table TAB1 was created using the following statement: CREATE TABLE tab1 (c1 INT, c2 INT, c3 INT, c4 INT, c5 INT); If column C1 is unique and queries typically access columns C1, C2 and C3 together, which statement(s) will createindex(es) that will provide optimal query performance?（）

A、CREATE UNIQUE INDEX xtab1 ON tab1 (c1); CREATE INDEX xtab2 ON tab1 (c2) INCLUDE (c3)    B、CREATE UNIQUE INDEX xtab1 ON tab1 (c1) INCLUDE (c2, c3)   C、CREATE UNIQUE INDEX xtab1 ON tab1 (c3, c2, c1)    D、CREATE UNIQUE INDEX xtab1 ON tab1 (c2) INCLUDE (c1, c3)  

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第9题
[多选题] Which of the following describe the process identifier that is used to run OSPF on a router? （）

A、It is locally significant.  B、It is globally significant.  C、It is needed to identify a unique instance of an OSPF database.  D、It is an optional parameter required only if multiple OSPF processes are running on the router.  E、All routers in the same OSPF area must have the same process ID if they are to exchange routing information.  

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第10题
[多选题] Which of the following describe the process identifier that is used to run OSPF on a router?（）

A、It is locally significant.  B、It is globally significant.  C、It is needed to identify a unique instance of an OSPF database.  D、It is an optional parameter required only if multiple OSPF processes are running on the router.  E、All routers in the same OSPF area must have the same process ID if they are to exchange routing information.  

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