Interview Questions

A collection just like an array is an ordered group of elements of the same type. Each elements position is determined by a unique subscript.

Index by tables:- They are similar to hash arrays that allows to search for subscript values using arbitrary numbers and strings.

They can be declared as:

TYPE type_name IS TABLE OF element_type [NOT NULL]

INDEX BY [BINARY_INTEGER | PLS_INTEGER | VARCHAR2(size_limit)];

INDEX BY key_type;

Example:

TYPE studenttyp IS TABLE OF emp%ROWTYPE

INDEX BY BINARY_INTEGER;

stud_tab studenttyp;

Nested tables:- they hold random number of elements and use sequential numbers as sub scripts.

They can be declared as:

TYPE type_name IS TABLE OF element_type [NOT NULL];

Example: TYPE employee_type IS TABLE OF NUMBER INDEX BY VARCHAR2(64);

Varrays: Holds a fixed number of elements which can be changed in run time. 

They can be declared as:

TYPE type_name IS {VARRAY | VARYING ARRAY} (size_limit) OF element_type [NOT NULL];

Example: TYPE Calendar IS VARRAY(366) OF DATE;

PL/SQL is Procedural Language SQL that is an extension of SQL that results in a more structural language composed of blocks. It is mainly used in writing applications that needs to be structured and has error handling.

A foreign key is a reference to another table. It is used to establish relationships between tables. For example, relationship between employee and professor table. One employee can have multiple professors. The Primary key of employee becomes foreign key of professor.
Example:
create table employee ( id number NOT NULL, professor_id NOT NULL, Name varchar(200) Constraint prim_id Foreign key(id) references professor(professor_id) );

By default, primary key creates a clustered index on the column, whereas a unique key creates a non clustered index by default.

A31. The self-referencing constraint limits in a single table the changes to a primary key that the related foreign key defines. The foreign key in a self referencing table must specify the DELETE CASCADE rule.

You should not use AJAX if:

             =>  You want the page to show in a search engine, such as Google, because WebCrawler does not execute JavaScript code.

             =>  The browser does not support JavaScript.

             =>  You want to create a secure application.

The interviewer is listening for an answer that indicates you've given this some thought and are not sending out resumes just because there is an opening. For example, "I've selected key companies whose mission statements are in line with my values, where I know I could be excited about what the company does, and this company is very high on my list of desirable choices."