Oracle SQL Interview Questions Series 1 [Basic]

Oracle SQL Interview Questions Series - 1

Oracle SQL Interview Questions covered in Eduflee, so complete all the series to get placed into the IT company.

At present Structured Query Language is very important to enter into the Software company.

After completing all the Interview series, you can crack many interviews with 100% assurance from my experience.

Basic Questions for SQL interview

• Schema => User
• Records => Rows
• Fields => Columns
• Result set => Output

1, What are the Schema Objects in Oracle SQL ?

    Table, View, Materialized view, Sequence, Synonyms, Index are the schema objects in SQL.

    Table => Basic Unit of Storage [Rows and Columns]

    View => Logical Representation of subject of records, It does not contains any data. So here data is logical.

    Materialized View =>  It contains the data, it is also called as Snapshot. It contains data physically.

    Sequence => It is a Numeric Value Generator

    Synonyms => used to provide alternate name to any object

    Index => It is used to retrieve the data easily by creating index and tuning the particular SQL query. 

    

2, What is Dual Table ?

    Dual Table is similar to a dummy table, which is used to process our own data

    

3, What is the data type used in Dual table ?

    It contain s VARCHAR2 data type in dual table.

4, SELECT * FROM dual; ?

    The above query will gives the output as "X"

5. Why Comment is used for ?

• Comment is used as Back up
• It is user friendly for developers, so if any changes done means with the help of 

6. Difference between Writing Order and Execution Order in Oracle SQL ? 

                                                

Writing Order	Execution Order
The writing Order is starts from  SELECT FROM WHERE GROUP BY HAVING ORDER	The Execution Order is starts from:- FROM WHERE GROUP BY HAVING SELECT ORDER

7) How to check whether the table is belongs to that owner or schema ?

By Using user_tables or all_tables , is used to check whether that table is present in that schema or not.

8) What is the mean by 'i', 'g', 'c' in Oracle version ?

   i, g, c are versions which are used in oracle, and it means that 'i' denotes the internet, 'g' denotes the grid computing and 'c' is for cloud computing.

Examples: Some of the Oracle versions are 8i, 10G, and 12C.

9) When and by whom was oracle founded ?

In the year 1977, oracle was founded by Larry Ellison, Bob Miner and Ed Oates.

10) Output for this Query : SELECT NULL + 22 FROM dual;

Answer : NULL, When Null is used with any other operator, it will shows the output as NULL.

11) Output for the below Query :

Answer : 

    SELECT COUNT(NULL) FROM dual;

    output: 0 "zero"

    SELECT COUNT(1) FROM dual;

    output: 1

    SELECT COUNT(100) FROM dual;

    output: 1

    SELECT COUNT(NULL) + 50 FROM dual;

    output: 50 

12) Difference between DBMS and RDBMS ?

    DBMS => Database management System

    It is used to access only single user. And there is no relationship between one to another or one to many data. And this DBMS is less security level when compared to RDBMS.

    RDBMS => Relational Database Management System.

    It is used to access multiple users at a time and the data related to one to one and one to many relationship model. And this RDBMS is maintained by tables [rows and columns]. It comes with high security level.

13) Where data are stored in Database ?

    Tablespace and Datafiles.

    In table space data are stored logically and in data files data are stored as a physical files.

14) How to find current date and current time using SQL ?

15) How to get the unique records in a particular column in a simple way using SQL ?

    SELECT  DISTINCT column_name FROM dual;

There are many ways to get the duplicates and distinct is one of the way to get the duplicate records.

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