Oracle InterViewQusetions 11-15

11. what is null value?
Null Value is neither zero nor it is a blank space. It is some unknown value which occupies 4 bytes of space of memory in SQL.

12. Define transaction?
A transaction is a sequence of SQL statements that Oracle Database treats as a single unit.

13. what is the difference between sql&oracle?
SQL is Stuctured Query Language.Oracle is a Database.SQL is used to write queries against Oracle DB.

14. What are different Oracle database objects?
TABLES
VIEWS
INDEXES
SYNONYMS
SEQUENCES
TABLESPACES

15. What is hash cluster?
A row is stored in a hash cluster based on the result of applying a hash function to the row's cluster key value. All rows with the same hash key value are stores together on disk.

Oracle InterView Questions 6-10

6. What is the difference between clustered and a non-clustered index?
A clustered index is a special type of index that reorders the way records in the table are physically stored. Therefore table can have only one clustered index. The leaf nodes of a clustered index contain the data pages.
A Non clustered index is a special type of index in which the logical order of the index does not match the physical stored order of the rows on disk.

7. What is a Table-space?
A database is divided into Logical Storage Unit called tablespace. A tablespace is used to grouped related logical structures together.

8. Why use materialized view instead of a table?
Materialized views are basically used to increase query performance since it contains results of a query. They should be used for reporting instead of a table for a faster execution.

9. What does ROLLBACK do?
ROLLBACK retracts any of the changes resulting from the SQL statements in the transaction.

10. Compare and contrast TRUNCATE and DELETE for a table?
Both the truncate and delete command have the desired outcome of getting rid of all the rows in a table. The difference between the two is that the truncate command is a DDL operation and just moves the high water mark and produces a now rollback. The delete command, on the other hand, is a DML operation, which will produce a rollback and thus take longer to complete.

Oracle InterView Questions

1.what is Oracle 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.

2. What are Clusters?
Clusters are groups of one or more tables physically stores together to share common columns and are often used together.

3. What is an Index?
An Index is an optional structure associated with a table to have direct access to rows, which can be created to increase the performance of data retrieval. Index can be created on one or more columns of a table.

4. 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 perspective from that of the base table
• Store complex queries.

5. What are the various types of queries?
The types of queries are :

• Normal Queries
• Sub Queries
• Co-related queries
• Nested queries
• Compound queries