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Ask the Expert

Q: What is the major difference between the clob and blob data types in Oracle Database 10g?

A: The clob stores only alphanumeric data, whereas the blob can accommodate any type of data, including sound and video.

Q: When specifying the number data type, how is the total length of the field determined?

A: The total length of a numeric field is determined by the digit(s) to the left of the comma if the specification includes an integer and decimal component. For example, number(4,1) denotes a maximum of four digits, of which one digit can be stored to the right of the decimal point.

Q: Which of the Oracle Database 10g background processes is responsible for writing information from memory into the database files?

A: This is the job of the database writer, or dbwr, process.

Q: Where does Oracle Database 10g read its environment from as it is started?

A: The startup parameters are read from the system parameter file, which can be a binary file stored in the Oracle Database 10g.

Q: As sessions interact with the data in the Oracle Database 10g, what role does the undo tablespace play in the architecture of the software?

A: When transactions change the contents of information in Oracle Database 10g's tables, this special tablespace keeps a ''before image" of the changes in case the operator decides to back out before saving newly entered information.

Views

Views are predefined subsets of data from an Oracle Database 10g table. The SQL query that builds the view is stored in the data dictionary and need not be reassembled every time the view is used. Suppose a personnel application stores the location of all employees in its EMPLOYEE_MASTER table in the loc_id column. With Oracle Database 10g, you can define a view called emp_hq as follows:

create or replace view emp_hq
as select * from employee_master
where loc_id = '2';

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