SQL Commands

1. Data Definition Language (DDL): It changes the structure of the table by creating, deleting, or altering the table. DDL commands are auto-committed, meaning they save all changes in the database.

Create: This command is used to create a new table in the database.

Create table Student;

Drop: This command is used to delete both the records and the structure of the table.

Drop table Student;

Alter: This command is used to change the structure of the table. It can modify an existing attribute or add a new one.

alter table Student 
rename column name to stud_name;           //renaming the column name

alter table Student
add gender char(1);                       //adding new attribute

alter table Student
modify gender varchar(6);                  //changing the size

Truncate: Deletes all rows in the table.

Truncate table Student;

2. Data Manipulation Language (DML): These commands are used to modify the database. They are not auto-committed, meaning changes are not permanently saved.

   Insert: This command is used to add data into a row of the table.

    Insert into Student values(1, "A", 21, "XYZ"),(2, "B", 22,"PQR")(3, "C", 21, "PQR"):;
   

   Update: This command is used to update or modify the values of a column in a table.

    Update Student set age=null
    where id=2;
   

   Delete: This command is used to remove one or more rows from a table.

    Delete from Student
    where id=3;
   

3. Data Query Language (DQL): This command fetches data from the table.

   Select: This command is used to display the contents of the table.

Select * from Student;

I have referred to various resources to understand and simplify it. Other commands will be covered in the next blog.