测试一下自己，看看自己会做这些数据库试题吗。（全部是面试题）。。

dd_wangy 2005-08-28 10:50:54

1.With respect to a relational table, what is a key?
(a) A minimal subset of columns that uniquely identifies a row in the table (b) The ID and password needed to access the table (c) The subset of all the rows and columns in the table that are visible to all users in the database system (d) The one column that uniquely identifies a row in the table

2.Which of the following is true about the number of primary keys and alternate keys with respect to a table?
(a) There can be many primary keys, but only one alternate key. (b) There can be only one primary key, but many alternate keys. (c) There can be only one primary key and only one alternate key. (d) There can be many primary keys and many alternate keys.

3.An insertion operation will _____ if the insertion violates the uniqueness property of a key.
(a) succeed with warning (b) crash the system (c) fail (d) succeed without warning

4.An insertion operation will _____ if the inserted primary key has a NULL value.
(a) succeed with warning (b) succeed without warning (c) fail (d) crash the system

5.For two tables to be union compatible, corresponding columns from each table should have which of the following?
(a) different domains (b) different names (c) the same domain (d) the same name

6.In the relational model, which of the following is true about the data type of a column?
(a) It need not be atomic and it cannot be an abstract data type. (b) It must be atomic and it cannot be an abstract data type. (c) It need not be atomic and it can be an abstract data type. (d) It must be atomic and it can be an abstract data type.

7.What is an alternate key?
(a) Any key that is not a primary key (b) The key to use when the primary key does not work (c) A key that was added to the table after the table was designed (d) A key that will become the primary key when the primary key is deleted

8.What does a projection operation do?
(a) It extends the number of columns in a table. (b) It selects rows from a table. (c) It extends the number of rows in a table. (d) It selects columns from a table.

9.The result of a set difference operation r - s will be
(a) tuples in r after deducting their values by the corresponding values in the tuples in s (b) tuples in s after deducting their values by the corresponding values in the tuples in r (c) those tuples that are in s but not in r (d) those tuples that are in r but not in s

10.Which of the following is true about primary keys and foreign keys holding NULL value?
(a) A primary key can hold a NULL value and a foreign key cannot hold a NULL value (b) A primary key cannot hold a NULL value and a foreign key cannot hold a NULL value (c) A primary key can hold a NULL value and a foreign key can hold a NULL value (d) A primary key cannot hold a NULL value and a foreign key can hold a NULL value

11.In contrast to _____ tables, a view refers to _____.
(a) base, a virtual table (b) empty, non-empty tables (c) non-empty, empty tables (d) virtual, base tables

12.When removing a table from the schema, using the CASCADE option would
(a) remove the table and all references to it (b) recursively remove the table and all other tables that the removed table refers to (c) remove the table and all other tables that the specified table refers to. (d) remove the table if there are no references to it

13.In a transaction, COMMIT specifies that
(a) all updates (including inserts, deletes, modifications) of a transaction are about to be made permanent in the database (b) all updates (including inserts, deletes, modifications) of a transaction are to be made permanent in the database (c) only the inserts and deletes of a transaction are to be made permanent in the database (d) only the inserts and deletes of a transaction are about to be made permanent in the database

14.Which of the following is true about the physical storage of tables defined by views?
(a) Extra physical storage is needed for storing the tables defined by views, only if views define additional non-existing columns. (b) There is no extra physical storage needed to store tables that a view defines. (c) Extra physical storage is always needed to store tables that a view defines. (d) Extra physical storage is needed to store tables that a view defines, only when rows are inserted into the view.

15.Which of the following SQL commands can be used to change, add, or drop column definitions from a table?
(a) MODIFY TABLE (b) UPDATE TABLE (c) CHANGE TABLE (d) ALTER TABLE

16.Which of the following SQL commands can be used to destroy and remove a table from the schema?
(a) DROP TABLE (b) DESTROY TABLE (c) REMOVE TABLE (d) DELETE TABLE

17.In SQL, which of the following operators are used to check for set membership in a SELECT statement?
(a) MEMBER and NOT MEMBER (b) IN and NOT IN (c) SUBSET and NOT SUBSET (d) COMPONENT and NOT COMPONENT

18.In SQL, the results of a _____ statement can be used to process a _____ statement.
(a) INSERT, SELECT (b) SELECT, INSERT (c) INSERT, DELETE (d) DELETE, INSERT

19.In a transaction, a ROLLBACK is used to
(a) roll all the updates (including inserts, deletes, modifications) of an aborted transaction into the database (b) roll only the inserts and deletes of an aborted transaction into the database (c) discard all the updates (including inserts, deletes, modifications) of a transaction from the database (d) discard only the inserts and updates of a transaction from the database

20.When a string whose length is strictly less than n is entered as the value of a field whose SQL data type is CHAR(n), the system responds by
(a) padding the end of the string with spaces to length n before storing it (b) padding the end of the string with NULL characters to length n before storing it (c) re-prompting for the entry of a string whose length is exactly n (d) storing the string as is

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