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Common SQL Commands

                         

SQL commands are divided into categories like DML (Data Manipulation language), DDL (Data definition language), TCL (Tranction control language) and DCL (Data control language). Here are a list of SQL commands.

1. DML COMMANDS

INSERT
UPDATE
SELECT
DELETE

2.DDL COMMANDS
CREATE
ALTER
DROP

3.TCL COMMANDS
COMMIT
ROLLBACK

4.DCL COMMANDS
GRANT
REVOKE

The table given below (named Student) has two fields id and Name.

Student Table

id

Name

1

Ravi

2

Ajay

 The commands are based on this table:

1. DML COMMANDS

INSERT ROWS
The syntax for this command is

insert into tablename(colname1,colname2) values(value1,value2);

Example:

insert into Student (id, Name) values(1,'Ravi');

This statement is used to insert a row of data into Student table.

UPDATE ROWS
The syntax for this command is

update tablename set colname1=colvalue where colname2=colvalue;

Example:

update Student set Name = 'Ajay' where id = 2;

This command has updated the Name 'Rose' in Student table whose id is 2.

SELECT ROWS
This command is used to select rows from a table.The syntax for this command is

select colname1,colname2 from tablename;

Example:

select Name from Student;

It will display all names from Student table. Like Ravi.

DELETE ROWS
The syntax for this command is-

delete from tablename where [search_conditions];

Example:

delete from Student where id=1;

This statement is used to delete the row from Student table where the student id is 1.

2. DDL COMMANDS

CREATE TABLE
This statement is used to create a table. The syntax for this command is

create table tablename (colname1 datatype [constraint], colname2 datatype [constraint]);

Example:

create table Student (id number(4) primary key, Name varchar2(20));

It creates the table Student which has two fields id i.e. Student id and Name i.e. the student name. The number and varchar2 are the data types of id and Name respectively. Field 'id' has the size 4 means it can take id up to 4 digits and same for Name, it can take the size up to 20 characters. And also added the constraint Primary key to the field 'id'.

ALTER TABLE
This command is used to add, drop columns in a table. The syntax for this command is

alter table tablename add colname1 datatype [constraint];
alter table tablename drop column colname1;

Example:

alter table Student add DOB date;

This command is used to add new field DOB in Student table. It's datatype is date. This is also used for drop column from the table. It will drop the DOB field by query given below-

Alter table Student drop column DOB;

DROP TABLE
The syntax for this command is-

drop table tablename;

Example:

drop table Student;

This statement is used for destroy the table from database.

3.TCL COMMANDS

COMMIT
This command is used for save the work done. The syntax is:

COMMIT;

ROLLBACK
This command is used to restore the database to original since the last commit. The syntax is-

ROLLBACK;

4. DCL COMMANDS

GRANT
This command is used for gives access privileges to users for database. The syntax is-

GRANT dba to username;

REVOKE
This command is used for withdraws access privileges to users for database. The syntax is-

REVOKE permissions on tablename from username;


                         

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