Versions - (PostgreSQL Advance)

PostgreSQL is a powerful and feature-rich open-source relational database management system. In this tutorial, we'll discuss how to manage versions in PostgreSQL, including syntax, example, output, explanation, use, important points, and summary.

Syntax

CREATE [TEMPORARY] [UNLOGGED] TABLE table_name (
    column_definitions
) [INHERITS (parent_table)];

ALTER TABLE table_name RENAME TO new_table_name;

DROP TABLE [IF EXISTS] table_name;

Example

Let's create and manage versions of a table in PostgreSQL.

-- Create the first version of a table
CREATE TABLE employees (
    id SERIAL PRIMARY KEY,
    name TEXT,
    email VARCHAR(255),
    phone VARCHAR(20)
);

-- Create a second version of the table with an additional column
CREATE TABLE employees_v2 (
    id SERIAL PRIMARY KEY,
    name TEXT,
    email VARCHAR(255),
    phone VARCHAR(20),
    department TEXT
);

-- Rename the second version of the table
ALTER TABLE employees_v2 RENAME TO employees;

-- Add a column to the first version of the table
ALTER TABLE employees ADD COLUMN salary DECIMAL(10, 2);

-- Drop the second version of the table
DROP TABLE IF EXISTS employees_v2;

Explanation

In this example, we created two versions of a table named "employees". The first version had three columns: "id", "name", "email", and "phone". We then created a second version of the table named "employees_v2" with an additional column named "department". We renamed the second version of the table to "employees", effectively replacing the first version.

Next, we added a column named "salary" to the first version of the table using the ALTER TABLE command. Finally, we dropped the second version of the table using the DROP TABLE command.

Use

Versions in PostgreSQL can be useful when you need to make changes to a table without affecting the data in the existing table. Instead, you can create a new version of the table with the changes you want to make and gradually transition to the new version.

Important Points

• Versions of a table can be created using the CREATE TABLE command with a different name for the new version.
• A version of a table can be renamed using the ALTER TABLE command with the RENAME TO clause.
• Columns can be added or removed from a version of a table using the ALTER TABLE command with the ADD COLUMN or DROP COLUMN clause.
• Versions of a table can be dropped using the DROP TABLE command with the IF EXISTS clause to avoid errors if the table does not exist.

Summary

In this tutorial, we covered how to manage versions in PostgreSQL. We discussed the syntax, example, output, explanation, use, important points, and summary of creating and managing versions of a table in PostgreSQL. With this knowledge, you can now use versions in PostgreSQL to make changes to a table without affecting the existing data in the table.