Technology Questions

A unique constraint on a column uniquely identifies the record by a combination of one or more fields. Few unique constraint fields can have a NULL value as long as the combination of values is unique.

Example:
create table employee ( id number NOT NULL, dob DATE, professor_id NOT NULL, Name varchar(200) Constraint id_unique UNIQUE(id,dob) );

Package is a collection of related classes and interfaces. package declaration should be first statement in a java class.

ClassName refName = new ClassName();

or

ClassName refName;

refName = new ClassName();

- SVG is the abbreviation for Scalable Vector Graphics and is recommended by W3C. 

- It is used to define vector-based graphics for the Web

- The graphics are defined in XML format

-An important quality of SVG graphics is that their quality is maintained even when they are zoomed or resized. 

- All the element and attributes of SVG files can be animated

A record data type represents a data type for that row in a database table. It lets u define your own records and not your own fields.

The server version of a Windows operating system is designed to provide more optimized networking services over a network. It can manage domains better and it includes more security feature and data backup support. Workstation versions act merely as clients and therefore do not need to have as much resources when compared to the server versions.

The UTL_FILE database package can be used to read and write operating system files. You need to have read /write access rights in that directory before the package can be used.

Example to write file:

Fhandler is a variable of type UTL_FILE.FILE_TYPE

UTL_FILE.PUTF(fHandler, 'Im writing to a file\n');

Example to read file:

UTL_FILE.GET_LINE(fHandler, buf);

Cursors help you manipulate the information retrieved by select statements. This can be done by assigning a name to the cursor.

Example:

CURSOR emp_cur 

IS 

SELECT emp_number from employee_tbl where employee_name = name_in;

Types of Cursors:

Implicit cursors- These cursors are not declared by the programmer. They are issued when the SQL statement is executed. The open, close and fetching is done by itself.

Example:

UPDATE employee SET salary = salary * 2.1;

Here, an implicit cursor is issued to identify the set of rows in the table which would be affected by the update.

Explicit cursors- These cursors are defined by programmer. They are used in queries that return multiple rows.

Example:

CURSOR emp_cur 

IS 

SELECT emp_number from employee_tbl where employee_name = name_in;