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SQL commands and syntax

SQL commands are divided into several different types, among them data manipulation language (DML) and data definition language (DDL) statements, transaction controls and security measures. The DML vocabulary is used to retrieve and manipulate data, while DDL statements are for defining and modifying database structures. The transaction controls help manage transaction processing, ensuring that transactions are either completed or rolled back if errors or problems occur. The security statements are used to control database access as well as to create user roles and permissions.

Let Learn about some No SQL

What is NoSQL ?

NoSQL is an upcoming category of Database Management Systems. Its main characteristic is its non-adherence to Relational Database Concepts. NOSQL means “Not only SQL”.

Concept of NoSQL databases grew with internet giants such as Google, Facebook, Amazon etc who deal with gigantic volumes of data.

When you use relational database for massive volumes of data , the system starts getting slow in terms of response time.



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To overcome this , we could of course “scale up” our systems by upgrading our existing hardware.

The alternative to the above problem would be to distribute our database load on multiple hosts as the load increases.

This is known as “scaling out”.

NOSQL database are non-relational databases that scale out better than relational databases and are designed with web applications in mind.

They do not use SQL to query the data and do not follow strict schemas like relational models.With NoSQL, ACID (Atomicity, Consistency, Isolation, Durability) features are not guaranteed always
Some Important Questions of SQL Database are listed Bellow :


1- State true or false. EXISTS, SOME, ANY are operators in SQL.

Answer: True

Explanation:

2- State true or false. !=, <>, ^= all denote the same operation.

Answer: True

Explanation:

3- What are the privileges that can be granted on a table by a user to others?

Answer: Insert, update, delete, select, references, index, execute, alter, all

Explanation:



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4- What command is used to get back the privileges offered by the GRANT command?

Answer: REVOKE

Explanation:

5- Which system tables contain information on privileges granted and privileges obtained?

Answer: USER_TAB_PRIVS_MADE, USER_TAB_PRIVS_RECD

Explanation:

6- Which system table contains information on constraints on all the tables created?

Answer: USER_CONSTRAINTS

Explanation:

7- TRUNCATE TABLE EMP; DELETE FROM EMP;
Will the outputs of the above two commands differ?

Answer: Both will result in deleting all the rows in the table EMP.
Explanation:

8- What is the difference between TRUNCATE and DELETE commands?

Answer: TRUNCATE is a DDL command whereas DELETE is a DML command. Hence DELETE operation can be rolled back, but TRUNCATE operation cannot be rolled back. WHERE clause can be used with DELETE and not with TRUNCATE.
Explanation:

9- What is the advantage of specifying WITH GRANT OPTION in the GRANT command?

Answer: The privilege receiver can further grant the privileges he/she has obtained from the owner to any other user.
Explanation:



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10- What does the following query do?

SELECT SAL + NVL(COMM,0) FROM EMP;

Answer: This displays the total salary of all employees. The null values in the commission column will be replaced by 0 and added to salary.
Explanation:


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