full notes about sql | learn what is sql?

 What is SQL?

• sql is stand for structured query language.
• This database language is mainly designed for
maintaining the data in relational database management
systems.
• sql is standard language for accessing and manipulating
database.

Types of SQL Commands:

DDL COMMANDS:

• DTM (Data Defined Languages ) used to change the
structure of the table Like creating the table, altering the
table & Deleting the table.
• All the commands in the DDL are auto Committed that
means it permanently save all the changes in the database.

1. CREATE:
This command is used to create a new database or table.

Syntax :

CREATE TABLE table_name(
column1 datatype,
column2 datatype,
column3 datatype,
......
):

Example:

CREATE TABLE Employee
(
EmployeelD int;
FirstName varchar(255),
LastName varchar(255),
AddressLine varchar(255),
City varchar(255)

2. UPDATE:

The UPDATE statement is used to modify the existing records in a table.

Syntax:
UPDATE table_name
SET colomn1 = valuel, colomn2 = value2, ...
WHARE CustomerlD = 101;

Example:
UPDATE Customers
SET ContactName ='iamrupnath', City ='Kolkata'
WHERE CustomerlD = 101;


3. DELETE:
The DELETE statement is used to delete the existing records in a table.
Syntax:
DELETE FROM table_name[WHERE Conditionl;
Example:
DELETE Customers wHERE CuntomerName = "developers_uni";

4. TRUNCATE:

A truncate SQL statement is used to remove all rows (complete data)
from a table. It is similar to the DELETE statement with no WHERE clause.

Syntax:
TRUNCATE TABLE table_name;
Example:
TRUNCATE TABLE Employee;

DML COMMANDS:

1. INSERT:
SQL INSERT statement is a SQL query. It is used to insert a single or a
multiple records in a table.

Syntax:
INSERT INTO table_name
VALUES (valuel, value2, value3 .....

Example:
INSERT INTO STUDENTS (ROLL_NO, NAME, AGE, CITY)
VALUES (1, developers_uni, 21, Kolkata)

3. ALTER:

The ALTER TABLE statement in Structured Query Language
allows you to add, modify, and delete columns of an existing
table.

Syntax:
ALTER table_name
ADD column_name datatype;

Example:
ALTER TABLE EMPLOYEE
ADD Email varchar (255);


4. DROP:

The DROP TABLE statement is used to drop an existing table in a
database. This command deletes both the structure & Records
Stored in the table.

Syntax:
DROP TABLE table_name;

Example:
DROP TABLE Employee

TCL COMMANDS:


1. COMMIT :

Commits a Transaction. The COMMIT command saves all the
transactions to the database since the last COMMIT or ROLLBACK
command.

Syntax:
COMMIT;

Example:
DELETE FROM Student WHERE AGE =21;
COMMIT:

2. ROLLBACK:

If any error occurs with any of the SQL-grouped statements, all
changes need to be aborted. The process of reversing changes is
called rollback

Syntax:
ROLLBACK;

Example:
DELETE FROM Student WHERE AGE= 21;
ROLLBACK;

DCL COMMANDS:

1. GRANT:

It is used to give user access privileges to a database.

Syntax:
GRANT SELECT, UPDATE ON MY_TABLE TO SOME_USER,
ANOTHER_USER;

2. REVOKE:

GRANT SELECT, UPDATE ON MY_TABLE TO SOME_USER<
ANOTHER_USER;

Syntax:
REVOKE SELECT, UPDATE ON MY_TABLE FROM USER!, USER2;