SQL Queries - DDL Commands

SQL Queries - DDL Commands

• 1.
  Program No. #01 Object :- Write SQL Queries for DDL (Data Definition Language) Statement. DDL Commands :-  CREATE Query  ALTER Query  TRUNCATE Query  RENAME Query  DROP Query 1. CREATE Command :- CREATE is a DDL SQL Command used to create a table or a database in relational database management system.  Creating a Database:- To create a database in RDBMS, Create command is used.Following is the syntax:-  Example for creating Database:-  Creating a Table:- CREATE command can also be used to create tables. Now when we create a table. We have to specify the names and datatypes of various columns in the Create command itself. Following is the syntax:- CREATE DATABASE DATABASE_NAME; CREATE DATABASE DBMS; CREATE TABLE TABLE_NAME ( Column_name1 datatype(size), Column_name2 datatype(size), Column_name3 datatype(size), Column_name4 datatype(size) );
• 2.
   Example forcreating Table:- 2. Alter Command :- ALTER command is used for altering the table structure, such as,  To add a column to an existing table.  To change datatype of any column or to modify its size.  To drop a column from table.  Adding new columns :- Using ALTER command we can add single or multiple new columns to any existing table. Following is the syntax:-  Here is an Example for this :- CREATE TABLE Student ( Roll_No. INT(15), Name CHAR(50), Branch CHAR(25) ); ALTER TABLE table_name ADD ( Column_name1 datatype(size), Column_name2 datatype(size), Column_name3 datatype(size) ); ALTER TABLE Student ADD ( Father_Name CHAR(60), Mother_Name CHAR(60), Address CHAR(100) );
• 3.
   Modifying anexisting column :- ALTER command can also be used to modify datatype of any existing column. Following is the syntax:-  Here is an Example for this:- 3. TRUNCATE Command :- TRUNCATE command removes all the records from a table, But this command will not destroy the table’s structure. When we use TRUNCATE command on a table its (auto-increment) primary key is also initialized. Following is its syntax:-  Here is an Exapmle :- 4. RENAME Query:- RENAME command is used to set a new name for any existing table. Following is the Syntax:-  Here is an Example :- ALTER TABLE table_name MODIFY Column_name datatype (Size); ALTER TABLE STUDENT MODIFY Address VARCHAR (200) ; TRUNCATE TABLE table_name ; TRUNCATE TABLE STUDENT ; RENAME TABLE STUDENT to STUDENT_INFO ; RENAME TABLE old_table_name to new_table_name ;
• 4.
  5. DROP Command:- DROP command completely removes a table from the database. This command will destroy the table structure and the data stored in it. Following is its Syntax:-  Here is an Example:- DROP command can also be used to delete the complete database. Following is its Syntax:-  Here is an Example :- DROP TABLE table_name ; DROP TABLE STUDENT ; DROP DATABASE database_name ; DROP DATABASE DBMS;