Managing Databases with Oracle Questions and Answers

Q: Oracle maintains a System Change Number (SCN) which is a database-wide value that is incremented by Oracle whenever database changes are made.

Correct answer: TrueThe system change number is a single database-wide counter, advanced as changes are committed and recorded in the redo stream and in every datafile header. Because it orders all changes across the whole database, it is what lets Oracle tell whether a set of files is mutually consistent and how far forward recovery must be applied.

Q: When you type into SQL*Plus and press enter, the statement will be finished and executed.

Correct answer: FalsePressing Enter simply moves to the next line of the buffer, so a statement can be spread over as many lines as is convenient for reading. Execution needs an explicit terminator: a semicolon at the end of the statement, or a slash on a line of its own to run whatever the buffer already holds.

Q: You can use the DROP statement to remove structures from the database.

Correct answer: TrueDROP removes a structure from the database entirely - DROP TABLE, DROP VIEW, DROP INDEX, DROP SEQUENCE. It is distinct from DELETE, which removes rows and leaves the table in place, and from ALTER, which changes a structure without removing it.

Q: Indexes are created to enforce uniqueness on columns and to enable fast retrieval by column values.

Correct answer: TrueBoth are genuine purposes and they often coincide. A unique index enforces the uniqueness of a primary key or unique constraint, and any index - unique or not - lets the optimiser find rows by column value without scanning the whole table. The cost is that every insert, update and delete must maintain the index as well as the table.

Q: Oracle does NOT support a CASCADE UPDATE constraint.

Correct answer: TrueOracle supports ON DELETE CASCADE but has no ON UPDATE CASCADE, so a change to a parent key value cannot be propagated to the children automatically. The remedy is either a trigger or, more usually, a surrogate primary key whose value never needs to change - which removes the problem rather than working around it.

Q: SQL*Plus is a text editor.

Correct answer: TrueSQL*Plus provides a small line editor for the statement buffer: LIST shows the lines with numbers, a line can be selected and changed with CHANGE, lines can be appended or deleted, and EDIT hands the buffer to a full external editor. It is a rudimentary facility rather than a text editor in the ordinary sense, but editing the buffer is part of what it does.

Q: Which prefixes are available to Oracle triggers?

Correct answer: Both :new and :oldA row-level trigger can refer to the values before the change with :old and after it with :new. Which are meaningful depends on the statement: an insert has only :new, a delete only :old, and an update both, which is what allows a trigger to compare the two and act on the difference.

11.

Of the three ways to create an Oracle database, which one is the easiest and most recommended?

A.Using the Oracle Database Configuration Assistant.
B.Using the Oracle-supplied database creation procedures.
C.Using the SQL CREATE DATABASE command.
D.None of the above is correct.

Answer: A

Correct answer: Using the Oracle Database Configuration Assistant.

The Configuration Assistant is a guided tool that creates the database, its files, its parameter file and its initial users in one operation, and it is the recommended route because it is difficult to omit a step. The CREATE DATABASE command gives complete control at the price of having to get every detail right by hand.

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12.

Oracle maintains a System Change Number (SCN) which is a database-wide value that is incremented by Oracle whenever database changes are made.

A.True
B.False

Answer: A

Correct answer: True

The system change number is a single database-wide counter, advanced as changes are committed and recorded in the redo stream and in every datafile header. Because it orders all changes across the whole database, it is what lets Oracle tell whether a set of files is mutually consistent and how far forward recovery must be applied.

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13.

Which of the following is not true about indexes?

A.Indexes are created to enforce uniqueness on columns.
B.Indexes are created to enable fast retrieval by column values.
C.Columns that are frequently used with equal conditions in WHERE clauses are good candidates for indexes.
D.Indexes are created with the ALTER TABLE command.

Answer: D

Correct answer: Indexes are created with the ALTER TABLE command.

Indexes are created with CREATE INDEX, and a unique index is also created implicitly when a primary key or unique constraint is declared. ALTER TABLE modifies the table, not the indexes on it. The other three statements are correct: indexes enforce uniqueness, speed retrieval, and are most worthwhile on columns frequently tested for equality.

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14.

When you type into SQL*Plus and press enter, the statement will be finished and executed.

A.True
B.False

Answer: B

Correct answer: False

Pressing Enter simply moves to the next line of the buffer, so a statement can be spread over as many lines as is convenient for reading. Execution needs an explicit terminator: a semicolon at the end of the statement, or a slash on a line of its own to run whatever the buffer already holds.

Discuss in Forum

15.

You can use the DROP statement to remove structures from the database.

A.True
B.False

Answer: A

Correct answer: True

DROP removes a structure from the database entirely - DROP TABLE, DROP VIEW, DROP INDEX, DROP SEQUENCE. It is distinct from DELETE, which removes rows and leaves the table in place, and from ALTER, which changes a structure without removing it.

Discuss in Forum

16.

Indexes are created to enforce uniqueness on columns and to enable fast retrieval by column values.

A.True
B.False

Answer: A

Correct answer: True

Both are genuine purposes and they often coincide. A unique index enforces the uniqueness of a primary key or unique constraint, and any index - unique or not - lets the optimiser find rows by column value without scanning the whole table. The cost is that every insert, update and delete must maintain the index as well as the table.

Discuss in Forum

17.

Oracle does NOT support a CASCADE UPDATE constraint.

A.True
B.False

Answer: A

Correct answer: True

Oracle supports ON DELETE CASCADE but has no ON UPDATE CASCADE, so a change to a parent key value cannot be propagated to the children automatically. The remedy is either a trigger or, more usually, a surrogate primary key whose value never needs to change - which removes the problem rather than working around it.

Discuss in Forum

18.

Which statement about sequences is not true?

A.A sequence is an object that generates a sequential series of unique numbers.
B.Sequences are most often used to provide values for surrogate keys.
C.NextVal and CurrVal are both sequence methods.
D.Sequences guarantee valid surrogate key values.

Answer: D

Correct answer: Sequences guarantee valid surrogate key values.

A sequence guarantees only that it will not hand out the same number twice. It cannot guarantee that the number is used, or used in the intended table, or that no one has inserted a conflicting value directly - numbers are also lost on rollback and on instance failure. The other three statements are correct descriptions of what a sequence is and does.

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19.

SQL*Plus is a text editor.

A.True
B.False

Answer: A

Correct answer: True

SQL*Plus provides a small line editor for the statement buffer: LIST shows the lines with numbers, a line can be selected and changed with CHANGE, lines can be appended or deleted, and EDIT hands the buffer to a full external editor. It is a rudimentary facility rather than a text editor in the ordinary sense, but editing the buffer is part of what it does.

Discuss in Forum

20.

Which prefixes are available to Oracle triggers?

A.:new only
B.:old only
C.Both :new and :old
D.Neither :new nor :

Answer: C

Correct answer: Both :new and :old

A row-level trigger can refer to the values before the change with :old and after it with :new. Which are meaningful depends on the statement: an insert has only :new, a delete only :old, and an update both, which is what allows a trigger to compare the two and act on the difference.

Discuss in Forum

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