Six Major DDL Commands in SQL - A Comprehensive Guide

In the realm of Structured Query Language (SQL), Data Definition Language (DDL) commands play a crucial role in defining and managing the structure of a database.

In this article, we’ll explore the usage of various DDL commands along with examples to provide a comprehensive understanding.

1. CREATE

The `CREATE` command is fundamental for establishing the foundation of a database by creating tables, schemas, or indices. Below is the syntax for creating a table:

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

The `ALTER` command is used to modify the structure of an existing table. It can add, modify, or delete columns or constraints. Here is the syntax for adding a new column:

ALTER TABLE Table_name ADD column_name datatype;

Example:

ALTER TABLE CUSTOMERS ADD email_id VARCHAR(50);

3. TRUNCATE

The `TRUNCATE` command is employed to delete all the data present in a table while keeping the table structure intact. It is a faster alternative to the `DELETE` command for removing all records.

TRUNCATE TABLE table_name;

Example:

TRUNCATE TABLE CUSTOMERS;

4. DROP

The `DROP` command is used to delete a table along with all its data. Exercise caution when using this command, as it irreversibly removes the table.

DROP TABLE table_name;

Example:

DROP TABLE CUSTOMERS;

5. RENAME

The `RENAME` command allows you to change the name of an existing table. This can be useful for maintaining a consistent naming convention or reflecting changes in the database structure.

RENAME TABLE table_name1 TO new_table_name1;

Example:

RENAME TABLE CUSTOMERS TO CUSTOMERINFO;

6. COMMENT

SQL supports both single-line and multi-line comments. Single-line comments start with “–,” while multi-line comments are enclosed within /* */.

Example:

-- Single-Line Comment

/* Multi-Line Comment
Line1,
Line2 */

Understanding and mastering these DDL commands is essential for effective database management. They provide the tools needed to create, modify, and maintain the structure of a database, ensuring it aligns with the evolving needs of an organization or application.

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Six Major DDL Commands in SQL – A Comprehensive Guide

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