Oracle Data Base Interview Questions Part-1

What is data?

Data is a collection of raw, facts and figures that is use in different place we can store anything in database is called data.

What is database?

Collection of organized data which can easily managed access, understand, and update.

What is database management system?

Any programming environment used to create containers, to manage human data, can be conceptualized as a Data Management System

What is table?

It is a set of elements that is consist of rows and columns in which we can store our data. In any table we define specified no, of columns and there are many no. of rows are available in table that is use for store the data row wise.

What is column?

Column is a one element of table that is use logically vertical shape in table. We define specified no. of columns in one table then store data in it.

What is row?

Rows are also second element of table that is use for store the data in table as a horizontally shape. We can enter many rows in one table. In database terms we can say one record to one row in table.

What is primary key?

A primary is uniquely identifies a row of the table this key ensure two things one is that null value does not allow and duplicate value also not allowed in table. A table must always have one and only one primary key. Primary key value is normally employee code, Driving license code, NIC code etc.

What is foreign key?

A foreign key is a references or a link between one table and another. The foreign key can be used to cross reference tables. A foreign has a link with parent table (that have primary key value). Suppose we have one table with primary key and w have second table that have foreign key and have a relation with parent table than we must enter the values in second table that is totally related with parent table.

What is unique key?

Unique key does not accept duplicate values but accept null values in oracle. Unique key is very much related with primary key in primary key we cannot enter NULL value and also duplicate value. But on the other hand in unique key we can enter NULL value but not duplicate value. For example in employee database we set Driving license no. unique because one employee have unique license no. and some employees have not.

What is the difference between primary key and unique key?

Unique key does not accept duplicate values but accept null values and primary key does not accept both two either NULL or duplicate data.

What is Null constraint?

The columns that have NULL constraint must fill with some data. A column in a table can be specified not null. It’s not possible to insert a null in such a column we cannot leave any column empty in tables that have NULL constraint. It should be fill with no matter with duplication of that.

What is the maximum no. of column in oracle table?

The maximum no. of columns is 255.

Is COMMIT statement can be use in database trigger?

We cannot use any transaction control statement (like commit, rollback, savepoint etc.) into the body of a trigger. But oracle provides a facility called Autonomous Transactions through which you can achieve this. You add that piece of the code, which contains commit, in some block and make that block as Autonomous Transaction and call or use that block into your trigger.

What are the components of Physical database structure of Oracle Database?

ORACLE database is comprised of three types of files. One or more Data files, two are more Redo Log files, and one or more Control files.

What are the components of Logical database structure of ORACLE database?

Tablespaces and the Database’s Schema Objects.

What is a Tablespace?

A database is divided into Logical Storage Unit called tablespaces. A tablespace is used to grouped related logical structures together.

What is SYSTEM tablespace and When is it Created?

Every ORACLE database contains a table space named SYSTEM, which is automatically created when the database is created. The SYSTEM tablespace always contains the data dictionary tables for the entire database.

What is schema?

A schema is collection of database objects of a User.

What are Schema Objects ?

Schema objects are the logical structures that directly refer to the database’s data. Schema objects include tables, views, sequences, synonyms, indexes, clusters, database triggers, procedures, functions packages and database links.

Can objects of the same Schema reside in different tablespaces.?

Yes.

Can a Tablespace hold objects from different Schemes ?

Yes.

what is Table ?

A table is the basic unit of data storage in an ORACLE database. The tables of a database hold all of the user accessible data. Table data is stored in rows and columns.

What is a View ?

A view is a virtual table. Every view has a Query attached to it. (The Query is a SELECT statement that identifies the columns and rows of the table(s) the view uses.)

Do View contain Data ?

Views do not contain or store data.

Can a View based on another View ?

Yes.

What are the advantages of Views ?

Provide an additional level of table security, by restricting access to a predetermined set of rows and columns of a table.

Hide data complexity.

Simplify commands for the user.

Present the data in a different perpecetive from that of the base table.

Store complex queries.