October 13, 2018

Sreekanth B

Wipro Most Frequently Asked Latest Oracle Interview Questions Answers

What are nested tables?

 Nested table is a data type in Oracle which is used to support columns containing multi valued attributes. It also hold entire sub table.

What is COALESCE function?

COALESCE function is used to return the value which is set to be not null in the list. If all values in the list are null, then the coalesce function will return NULL.

Coalesce(value1, value2,value3,…)

What is BLOB datatype?

A BLOB data type is a varying length binary string which is used to store two gigabytes memory. Length should be specified in Bytes for BLOB.

How do we represent comments in Oracle?

Comments in Oracle can be represented in two ways –

Two dashes(–) before beginning of the line – Single statement
/*—— */ is used to represent it as comments for block of statement

 Difference between varchar and varchar2 data types?

Varchar can store upto 2000 bytes and varchar2 can store upto 4000 bytes. Varchar will occupy space for NULL values and Varchar2 will not occupy any space. Both are differed with respect to space.

In which language Oracle has been developed?

Oracle has been developed using C Language.
Wipro Most Frequently Asked Latest Oracle Interview Questions Answers
Wipro Most Frequently Asked Latest Oracle Interview Questions Answers

What is RAW datatype?

RAW datatype is used to store values in binary data format. The maximum size for a raw in a table in 32767 bytes.

What is the use of NVL function?

The NVL function is used to replace NULL values with another or given value. Example is –

NVL(Value, replace value)

What is DML?

Data Manipulation Language (DML) is used to access and manipulate data in the existing objects.  DML statements are insert, select, update and delete and it won’t implicitly commit the current transaction.

What is key preserved table?

A table is set to be key preserved table if every key of the table can also be the key of the result of the join. It guarantees to return only one copy of each row from the base table.

What is WITH CHECK OPTION?

The WITH CHECK option clause specifies check level to be done in DML statements. It is used to prevent changes to a view that would produce results that are not included in the sub query.

What is the use of Aggregate functions in Oracle?

Aggregate function is a function where values of multiple rows or records are joined together to get a single value output. Common aggregate functions are –

Average
Count
Sum

How can we view last record added to a table?

Last record can be added to a table and this can be done by –

Select * from (select * from employees order by rownum desc) where rownum<2;
1
Select * from (select * from employees order by rownum desc) where rownum<2;

What is the data type of DUAL table?

The DUAL table is a one-column table present in oracle database.  The table has a single VARCHAR2(1) column called DUMMY which has a value of ‘X’.

What is difference between Cartesian Join and Cross Join?

There are no differences between the join. Cartesian and Cross joins are same. Cross join gives cartesian product of two tables – Rows from first table is multiplied with another table which is called cartesian product.

Cross join without where clause gives Cartesian product.

Can we store pictures in the database and if so, how it can be done?

Yes, we can store pictures in the database by Long Raw Data type. This datatype is used to store binary data for 2 gigabytes of length. But the table can have only on Long Raw data type.

What is an integrity constraint?

An integrity constraint is a declaration defined a business rule for a table column. Integrity constraints are used to ensure accuracy and consistency of data in a database. There are types – Domain Integrity, Referential Integrity and Domain Integrity.

What is an ALERT?

An alert is a window which appears in the center of the screen overlaying a portion of the current display.

What is hash cluster?

Hash Cluster is a technique used to store the table for faster retrieval. Apply hash value on the table to retrieve the rows from the table.

What are the various constraints used in Oracle?

Following are constraints used:

NULL – It is to indicate that particular column can contain NULL values
NOT NULL – It is to indicate that particular column cannot contain NULL values
CHECK – Validate that values in the given column to meet the specific criteria
DEFAULT – It is to indicate the value is assigned to default value

What are cursor attributes?

Each cursor in Oracle has set of attributes which enables an application program to test the state of the cursor. The attributes can be used to check whether cursor is opened or closed, found or not found and also find row count.

What are SET operators?

SET operators are used with two or more queries and those operators are Union, Union All, Intersect and Minus.

How can we delete duplicate rows in a table?

Duplicate rows in the table can be deleted by using ROWID.

What are the attributes of Cursor?

Attributes of Cursor are

%FOUND
Returns NULL if cursor is open and fetch has not been executed

Returns TRUE if the fetch of cursor is executed successfully.

Returns False if no rows are returned.

%NOT FOUND
Returns NULL if cursor is open and fetch has not been executed

Returns False if fetch has been executed

Returns True if no row was returned

%ISOPEN
Returns true if the cursor is open

Returns false if the cursor is closed

%ROWCOUNT
Returns the number of rows fetched. It has to be iterated through entire cursor to give exact real count.

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