What Is Data Definition Language (DDL) Exactly?
A data definition language (DDL) is a computer language for creating and reconfiguring database object structures. Views, schemas, tables, and indexes are examples of database objects.
In some contexts, this term is also known as “data description language” because it describes the fields and records in a database table.
Data Definition Language Explained by Hufpost (DDL)
DDL is now incorporated into any formal language used to describe data in the database industry. However, it is regarded as a subset of SQL (Structured Query Language). SQL frequently combines imperative verbs with normal English sentences to implement database changes. As a result, DDL does not appear as a different language in a SQL database, but it does define changes.
It interacts with database schema explanations to generate and customise the structure of objects in a database. Unlike data manipulation language (DML) commands, which are used to modify data, DDL commands are used to change the database structure, such as creating new tables or objects with all of their characteristics.
TABLE CREATION Employee Id (INTEGER PRIMARY KEY, CHAR (50) NULL, CHAR (75) NOT NULL);
Every command before the mandatory semi-colon at the end of the statement is processed. The data type is specified in this example by the string CHAR. Other data types include the date, number, and integer.
An alter command makes changes to an existing database table. This command can add new columns, remove existing columns, and even change the data type of columns in a database table.
Here is an indication of command syntax:
MODIFY the object type and name parameters;
As an example,
Employee PK) ADDED TO TABLE Employee
To add a constraint and enforce a unique value, we added a unique primary key to the table in this example. An employee PK is a primary key constraint on the employee table.
The drop command is used to delete objects like tables, indexes, and views. A drop statement cannot be reversed, so once an object is destroyed, it cannot be recovered.
Drop statement syntax is as follows:
REMOVE the object name and type;
As an example,
Employee Drop Table
We’re deleting the employee table in this example.
The TRUNCATE statement, like DROP, is used to quickly remove all records from a table. Unlike DROP, which completely destroys a table, TRUNCATE saves its entire structure to be reused later.
The TRUNCATE TABLE table name is the Truncate statement syntax.
As an example,
An employee of TRUNCATE TABLE
In this example, we’ve marked all of the employee table’s extents for deallocation, so they’re considered empty for reuse.
RENAME and COMMENT are two other commonly used commands. The first is used with the ALTER TABLE statement to change an object’s name (table, column, etc.). The COMMENT command is used to insert single-line, multi-line, and in-line comments.