DDL Commands

In this sub section, let us learn the usage of below commands with examples.

1. CREATE

CREATE command is used to create a table, schema or an index.

Syntax:

         CREATE TABLE table_name (
                column1 datatype,
                column2 datatype,
                ....);

Example:

        CREATE TABLE CUSTOMERS(
            InsuranceID INT,
            Name VARCHAR(50),
            DOB  DATE, 
            NIN INT, 
            Location VARCHAR(255)
        );

2. ALTER

ALTER command is used to add, modify or delete columns or constraints from the database table.

Syntax

ALTER TABLE Table_name ADD column_name datatype;

Example

 ALTER TABLE CUSTOMERS ADD email_id VARCHAR(50);

3. TRUNCATE:

TRUNCATE command is used to delete the data present in the table but this will not delete the table.

Syntax

TRUNCATE table table_name;

Example

TRUNCATE table CUSTOMERS;

4. DROP

DROP command is used to delete the table along with its data.

Syntax

DROP TABLE table_name;

Example

DROP TABLE CUSTOMERS;

5. RENAME

RENAME command is used to rename the table name.

Syntax

ALTER TABLE table_name1 RENAME to new_table_name1; 

Example

ALTER TABLE CUSTOMERS RENAME to CUSTOMERINFO;

6. COMMENT

Single-Line Comments:

Statements starting with -- are treated as single line comments.

Example:

 --Line1;

Multi-Line comments:

Statements enclosed in /**/ are treated as Multi-line comments

   /* Line1,
   Line2 */