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Oracle Interview Questions

An Overview of Oracle

ORACLE is primarily a relational database management system. Oracle is also known as Oracle DB or Oracle RDMS. By using Oracle, the user can directly access the objects through the Structured Query Language(SQL).

Oracle is designed to support multiple data models. The best part about Oracle is that it has its network component which allows the communications across the networks. Oracle runs on Windows, UNIX, Linux, and Mac OS. Oracle is written in Assembly language, C & C++.in today's world Oracle database is considered as one of the most reliable database engines in the world. Oracle interview questions we are mentioning below will help you to gain enough of the knowledge about Oracle.

Development History

  • Flashback Technology recovers the data which is lost or deleted efficiently
  • Reliable even when the tasks are demanding
  • Manages a large amount of data
  • Has the capability to maintain multiple databases.

All your questions related to Oracle will be answered in the Oracle interview questions for freshers mentioned below.

Development History

Oracle was developed by Lawrence Ellison and his co-workers Bob Miner and Ed Oates in the year 1977. The first version ORACLEv2 was released in the year 1979 which was the first available SQL based RDBMS.

Latest Version

Oracle Database 18c is the newest version which got released on 16th February 2018.

Oracle Interview Questions and answers

Looking for a new job? Do not miss to read our Oracle Interview Questions and answers. Whether you are a fresher or an experienced, these questions and answers that can help you to crack your interview.

Oracle is fundamentally a relational database management system. By using ORACLE, the user can directly access the objects through the Structured Query Language(SQL). Oracle is designed to support multiple data models. Oracle runs on Windows, UNIX, Linux, and Mac OS.Oracle is written in Assembly language, C & C++.

 

Because of the following reasons Oracle is the most used database software.

  • Flashback Technology:-Recovery of the data is done efficiently
  • ACID tool:-maintains the integrity of the information
  • Oracle can be used for small business applications as well as large business applications.

The latest version of Oracle Database is 18c. This version got released on 16th February 2018.

ORACLE was developed by Lawrence Ellison and his co-workers Bob Miner and Ed Oates

in the year 1977. The first version ORACLEv2 was released in the year 1979 which was the

first available SQL based RDBMS.

 

Here are some of the features of the ORACLE:-

  • Backup and Recovery of Data:-ORACLE provides Flashback technology which leads to efficient recovery of data.
  • Portable:-The ORACLE database has been ported to many platforms, and as a result, the applications on Oracle are safe when the OS is changed.
  • Speed:-Speed of the ORACLE database is good
  • Multiple Database Management:-ORACLE manages various databases at the same time. The user can quickly move at a place where data is actually stored from the node to node in a network
  • Efficient Data Integrity:-ORACLE uses the integrity constraints due to which invalid data entry is restricted to be entered into the database tables.
  • Provides Cursor Support:-With the help of cursor, programming becomes easy due to the row-to-row processing.
S.no SQL ORACLE
1. Use T-SQL (Transact-SQL) language Use PL/SQL(Procedural Language/ SQL) language
2. The database is shared among the users The database is not shared among the users
3. Complex but very powerful Simple and easy to implement

The TRUNCATE statement removes all the records from the table in the ORACLE database. If once the TRUNCATE statement truncate the table then the data cannot be recovered back.

Example

                                                

Syntax:- TRUNCATE TABLE table_name

PL/SQL is the language which is used to write the codes in the database.

For Example - PL/SQL is used to write the ORACLE database.PL/SQL is basically to combine the SQL and the procedural feature of the programming language. This language was developed to enhance the characteristics of the SQL language.

 

Some of the features of the PL/SQL are:-

  • PL/SQL functions can be called directly from the SQL.
  • PL/SQL can run without the involvement of human.
  • Programs can run on the different Operating Systems.
  • PL/SQL supports Loops, Conditions, and OOPS concepts.
S.no TRUNCATE DELETE
1. Rollback of the data is not possible Rollback of the data is possible
2. All the records are deleted Can delete a specific record using the WHERE condition.
3. Uses less transaction space Use more transaction space

An INSERT statement is used in the ORACLE database to insert the single record or the multiple records in a table.

This particular ORACLE interview question explains the importance of keys in the database.

Example

                                                

SYNTAX:-

INSERT INTO table (column1, column2, ... column_n ) VALUES

(expression1, expression2, ... expression_n );

An UPDATE statement is used to update the records that already exist in the table.

Example

                                                

SYNTAX:-

UPDATE table

SET column1 = expression1,

column2 = expression2,

  ...

column_n = expression_n

[WHERE conditions];

S.no SAP ORACLE
1. The language used is ABAP The language used is PL/SQL
2. It provides the tools for the flow of information in the business ORACLE is the multiple model database management system
3. The functional areas are Sales, Accounting, etc The functional areas are transaction processing, data warehousing, etc

Here is the list of Oracle12c new features:-

  • Pluggable Database:-This feature has changed the ORACLEdatabase architecture. In this, the Metadata is stored in the container database, and the user data is stored in the Pluggable Database.
  • Data Redaction:-This is the essential feature of 12C.Data Redaction basically means masking of the data.
  • RMAN command:-RMAN (Recovery Manager)command is used to restore a particular table which used to be a hard job before.
  • Multiple indexes:-Now, the column can be in more than one index. For example -Column can be included in the B-tree index as well as a Bit Map index but only one used at a time.

ORACLE 12c created the change in the architecture of the ORACLE database. In this version came with the concept of the Container Database (CDB) and the Pluggable Database (PDB)

  • Container Database (CDB) :- Container database contains the Oracle Metadata.This database includes control files, data files, temp files, etc. and this includes the data dictionary for those objects which are owned by the root container.
  • Pluggable Database (PDB):- Pluggable Database contains the data files and temp files to handle PDB's objects only, and this includes the data dictionary for those objects which are in PDB only.

This is the favorite interviewer question in Oracle interview questions for experienced.

  • Character Datatypes-CHAR, VARCHAR2, VARCHAR, NCHAR, NVARCHAR2, etc
  • Numeric Datatypes:-NUMBER, BINARY_FLOAT, BINARY_DOUBLE
  • DATE Datatype:-DATE, DD-MON-YY, TIMESTAMP, etc
  • LOB Datatypes:-BLOB, CLOB, NCLOB, etc
  • RAW and LONG RAW Datatypes
  • ROWID and UROWID Datatypes
  • ANSI, DB2, and SQL/DS Datatypes
  • XML Datatypes:-XMLType
  • URI Datatypes:-UriType
S.no SUBSTR (sub-string) INSTR (in-string)
1. It extracts the specific part of the string from the whole string It searches the entire string for finding the sub-string
2. The output data type is the number for the numeric input and the character for the date and the character input The output data type is always the number
3. The second argument is always the number The second argument should be a number or the character depending upon the data type of the input.
S.no REPLACE() TRANSLATE()
1. It replaces the complete string at once It replaces the character one by one
2. If no match is found, then it returns the string If no match is found, then it returns the NULL value.
3. REPLACE( string1, string_to_replace [, replacement_string] ) TRANSLATE( string1, string_to_replace, replacement_string )
S.no Primary Key Unique Key Foreign Key
1. Cannot have a NULL value It can have a NULL value It can accept the NULL value
2. It is a clustered index It is a non-clustered index The Index is manually created whether clustered or non-clustered
3. The Primary key can only be 1 in a table The Unique key can be more than 1 in a table The Foreign key can be more than 1 in a table

The trigger is the procedure which is implicitly executed by the Oracle server when the INSERT, UPDATE, DELETE statement is executed against the associated table in the Oracle database.

 

Based on the event these are the types of trigger:-

  • DDL Trigger:-INSERT/UPDATE/DELETE
  • DML Trigger:-CREATE/ALTER
  • DATABASE Trigger:-LOGON/LOGOFF/STARTUP/SHUTDOWN

The compound trigger was in introduced in Oracle 11g. This single trigger on a table enables the user to specify the actions for each of the four timing points:

  • Before the firing statement
  • Before each row that the firing statement affects
  • After each row that the firing statement changes
  • After the firing statement

In other words, Compound trigger merges all the four triggering events into the single piece of code, and as a result, the performance of the database server is improved during the bulk operations. The Compound trigger is only for the DML triggers.

The translate function replaces the characters in a string with the new set of characters one by one. For example:- the first character in the string is replaced by the first character of the original string and so on. The translate function always returns a string value.

Example

                                                

Syntax:-

TRANSLATE( string1, string_to_replace, replacement_string )

String1:-the string which has to be replaced

string_to_replace:-the string that has to be searched in the string 1

replacement_string:-the new string with which string1 will be replaced.

Once the table is created, then the user can add any value in the table, but the values have to be validated. In this case, the constraints act as a validator which checks the data validity.

There are five types of constraints:-
  • NOT NULL:-The column will not accept the NULL value
  • UNIQUE:-It will check whether the record entered is unique or not.
  • PRIMARY:-The column will have a value, and it will be unique. In a table, only one primary key should be there.
  • CHECK:-when the user wants the record in the column to be of a particular type.
  • FOREIGN KEY:-to relate more than one table that means matching the value of one table with that of another table.

Drop constraint is used for removing the constraints from the table.

Syntax:-

ALTER TABLE table_name

DROP CONSTRAINT constraint_name

Example

                                                

For example:- if the table name is INTERVIEW. QUESTIONS and the constraint name is TEST_ CONST

ALTER TABLE INTERVIEW. QUESTIONS
DROP CONSTRAINT TEST_ CONST

Dynamic SQL is the programming methods in which the SQL statements are constructed at the run time. Dynamic SQL is used when there is a requirement of the DDL(database definition language) statements while writing the programs or when the user is not aware of the compilation time of the SQL statement.

When the data required by the user is in more than one table, then Join comes into the picture. Oracle Join is used to combine the rows from more than one tables. Join also retrieves data from multiple tables and creates a new table.

Left join returns all the records from the left-hand side of the table which is specified in the ON condition, only those records from the right table where the join condition is met.

Example

                                                

syntax:-

SELECT columns

FROM table1

LEFT JOIN table2

ON table1.column = table2.column;

Example

                                                

Here is the syntax:-

SELECT columns

FROM table1

INNER JOIN table2

ON table1.column = table2.column;

An Inner join is also called a simple join, and it is the mostly used join.

A self join means in a table each row is joined to other rows in the table and also to itself

Here, the standard JOIN command is used in which both the tables in the join are the same tables.

Example

                                                

SELECT T2.name

FROM category T1

JOIN category T2

ON T2.parent = T1.id

WHERE T1.name = 'Best interview questions.'

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