Introduction to SQL - Part 3 - Data Definition Language

SQL Commands in Details 

Data Definition Language (DDL)

• DDL changes the structure of the table like creating a table, deleting a table, altering a table, etc.
• All the command of DDL are auto-committed that means it permanently save all the changes in the database.
• Here are some commands that come under DDL:

• CREATE

• It is used to create a new table in the database. 

  
  
• Syntax

                                CREATE TABLE TABLE_NAME (COLUMN_NAME DATATYPES[,....]);

• Example

• CREATE TABLE EMPLOYEE(Name VARCHAR2(20), Email VARCHAR2(100), DOB DATE);

• ALTER

• It is used to alter the structure of the database. This change could be either to modify the characteristics of an existing attribute or probably to add a new attribute.

• Syntax:

• ALTER TABLE table_name ADD column_name COLUMN-definition;
• ALTER TABLE MODIFY(COLUMN DEFINITION....);

• Example:
• ALTER TABLE STU_DETAILS ADD(ADDRESS VARCHAR2(20));
• ALTER TABLE STU_DETAILS MODIFY (NAME VARCHAR2(20));

• DROP

• It is used to delete both the structure and record stored in the table.

• Syntax:

• DROP TABLE {table Name};

• Example:

• DROP TABLE EMPLOYEE;

• TRUNCATE

• It is used to delete all the rows from the table and free the space containing the table

• Syntax:
• TRUNCATE TABLE table_name;

• Example:
• TRUNCATE TABLE EMPLOYEE;