Data Definition Language (DDL) in SQL

Data Definition Language (DDL), also known as Data Description Language, is a specialized computer language used to define the structure of databases and tables in SQL. It allows database administrators to create, modify, and remove database objects.

Creating Tables in SQL

One of the fundamental operations in SQL is creating tables using the CREATE TABLE statement. This statement defines the structure of a new table within a database.

When creating a table, you specify the name of the table, define the columns it will contain, specify the data types of each column, and set any constraints such as primary keys, foreign keys, or unique constraints.

The syntax for creating a table is as follows:

CREATE [TEMPORARY] TABLE [table name] ( [column definitions] ) [table parameters];

Understanding Referential Integrity in SQL

Referential integrity is a crucial concept in database management that ensures the accuracy and consistency of data between related tables. In SQL, maintaining referential integrity is essential for data reliability.

There are specific statements used to enforce referential integrity:

1. DROP objecttype objectname;: This statement is employed to drop a constraint or object in the database, thereby allowing modifications to the database structure.
2. ALTER objecttype objectname parameters;: This statement enables the alteration of attributes of an existing object in the database, such as columns or constraints.

By utilizing these statements effectively, database administrators can establish and maintain relationships between tables, ensuring data consistency and integrity within the database.