SQL DDL (Data Definition Language) queries with examples:

DDL stands for Data Definition Language. It is a subset of SQL (Structured Query Language) used for defining and managing the structure of a relational database. DDL commands enable database administrators and users to create, modify, and delete database objects such as tables, indexes, and views.

 

Here are details of some SQL DDL (Data Definition Language) queries with examples:

1. CREATE TABLE:
• Description: Used to create a new table in the database.
• Example:

CREATE TABLE employees (

 emp_id INT PRIMARY KEY,

emp_name VARCHAR(50),

emp_salary DECIMAL(10, 2)

);

2. ALTER TABLE:
• Description: Used to modify the structure of an existing table.
• Example:

ALTER TABLE employees

ADD COLUMN emp_department VARCHAR(30);

3. DROP TABLE:
• Description: Used to delete an entire table along with its data and structure.
• Example:

DROP TABLE employees;

4. CREATE INDEX:
• Description: Used to create an index to improve data retrieval efficiency.
• Example:

CREATE INDEX emp_name_index ON employees (emp_name);

5. ALTER INDEX:
• Description: Used to modify the structure of an existing index.
• Example:

ALTER INDEX emp_name_index RENAME TO emp_full_name_index;

6. DROP INDEX:
• Description: Used to remove an existing index.
• Example:

DROP INDEX emp_full_name_index;

7. TRUNCATE:

·    Description: Used to remove all rows from a table but retain its structure for future use.

• Example:

TRUNCATE TABLE employees;

 

8. COMMENT:

·         Description Used to add comments to the data dictionary.

·         Example:

COMMENT ON TABLE employees IS 'Table storing employee information';

 

DDL commands are powerful and have a significant impact on the database structure. They are typically executed by database administrators or users with the necessary privileges to manage the database schema.