Commands.md

Commands of SQL

1. Data Definition Language (DDL)

1. CREATE

    Used to create a table or database
   
          Syntax:  CREATE DATABASE DatabaseName
          Ex:          CREATE DATABASE School
   
          Syntax: CREATE TABLE TableName
          Ex:          CREATE TABLE Student

2. ALTER

   Used to change the structure of the table

   • Add a new column
     
            Syntax: ALTER TABLE TableName ADD ColumnName datatype(value)
            Ex:          ALTER TABLE Student ADD age NUMBER(2)
     

   • Remove an existing column
     
            Syntax: ALTER TABLE TableName DROP COLUMN ColumnName
            Ex:          ALTER TABLE Student DROP COlUMN address
     

   • Rename the existing column
     
            Syntax: ALTER TABLE TableName RENAME COLUMN oldColumnName TO newColumnName
            Ex:          ALTER TABLE Student RENAME COLUMN email TO emailid
     

   • Increase or decrease the column size
     
            Syntax: ALTER TABLE TableName MODIFY ColumnName datatype(newValue)
            Ex:          ALTER TABLE Student MODIFY emailid VARCHAR(30)
     

   • Change the column data type
     
            Syntax: ALTER TABLE TableName MODIFY ColumnName datatype
            Ex:          ALTER TABLE Student MODIFY DateofBirth year
     

3. TRUNCATE

   Removes all the rows from the table
   
          Syntax: TRUNCATE TABLE TableName
          Ex:          TRUNCATE TABLE Student

4. DROP

   Drops the entire table structure
   
          Syntax: DROP TABLE TableName
          Ex:          DROP TABLE Student

2. Data Manipulation Language (DML)

1. INSERT

   Insert rows to tables
   
          Syntax: INSERT INTO TableName(column1, column2,...) VALUES(value1, value2,...)
          Ex:          INSERT INTO Student(RollNo, Name, Age) VALUES (1, 'Srishti', 21)

2. UPDATE

   Modify existing rows in a table
   
          Syntax: UPDATE TableName SET ColumnName = value [WHERE condition]
          Ex:          UPDATE Student SET Age = 22 WHERE RollNo = 1;

3. SELECT

   Used to retrieve rows from a database or a table
   
          Syntax: SELECT ColumnName FROM TableName
          Ex:          SELECT Name FROM Student

4. DELETE

   Remove existing rows from the table
   
          Syntax: DELETE FROM TableName [WHERE condition]
          Ex:          DELETE FROM Student WHERE RollNo = 3;

3. Data Control Language (DCL)

1. GRANT

   Gives users access privileges to the database

2. REVOKE

   Withdraws the user’s access privileges given by using the GRANT command

4. Transaction Control Language (TCL)

1. COMMIT

   Commits a transaction

2. ROLLBACK

   Rollbacks a transaction in case of any error occurs

3. SAVEPOINT

   Sets a savepoint within a transaction