Volansys Technologies Interview Questions and Answers

DDL stands for Data Definition Language. It is used to define the structure of database objects.

• DDL commands are used to create, modify, and delete database objects such as tables, indexes, and views.

• Examples of DDL commands include CREATE, ALTER, and DROP.

• DDL commands are not used to manipulate data within the database, that is done using DML (Data Manipulation Language) commands.

Types of constraints include primary key, foreign key, unique, check, and default constraints.

• Primary key constraint ensures each row in a table is unique.

• Foreign key constraint enforces referential integrity between two tables.

• Unique constraint ensures that all values in a column are distinct.

• Check constraint restricts the values that can be inserted into a column.

• Default constraint provides a default value for a column if no value is specified.

A foreign key is a column or a group of columns in a database table that uniquely identifies a row in another table.

• A foreign key establishes a relationship between two tables in a database.

• It ensures referential integrity by enforcing a link between the data in the two tables.

• Foreign keys help maintain data consistency and prevent orphaned records.

• Example: In a database with tables for 'orders' and 'customers', the 'customer_id' in the 'orders' table can be a foreign key tha...read more