How To Change Column Data Types in PostgreSQL Without Losing Data || Pos...

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In this video, I will guide you through the process of changing column data types in PostgreSQL without losing any data. This tutorial is essential for anyone looking to update their database schema safely and efficiently, ensuring data integrity is maintained throughout the process.

In this tutorial, you’ll learn:

• Introduction to Data Type Changes: Understand the importance and common scenarios for changing column data types in PostgreSQL.

• Preparing for Data Type Changes: Learn how to prepare your database and data for changing column data types, including creating backups and understanding the implications of the change.

• Changing Column Data Types Safely: Step-by-step instructions on how to change column data types in PostgreSQL without losing data, including necessary SQL commands and best practices.

• Handling Common Data Type Conversions: Explore how to handle common data type conversions, such as converting between text, integer, and date types, with examples.

• Troubleshooting Data Type Change Issues: Tips for troubleshooting common issues that may arise during the data type change process, ensuring your database remains functional and data remains intact.

• Best Practices for Schema Changes: Gain insights into best practices for making schema changes, including minimizing downtime, validating changes, and testing thoroughly.

Whether you’re a database administrator, developer, or anyone responsible for managing PostgreSQL databases, this video provides valuable insights and practical advice to help you change column data types effectively and safely.

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Source Codes:

-- How To Change Column Data Types in PostgreSQL Without Losing Data

-- Case 1: Simple Data Type Change (e.g., INTEGER to BIGINT)

ALTER TABLE table_name

ALTER COLUMN column_name TYPE BIGINT;

-- Create the sample table with an INTEGER column

CREATE TABLE sample_table_int (

    id SERIAL PRIMARY KEY,

    some_integer INTEGER

);

-- Insert sample data into the table

INSERT INTO sample_table_int (some_integer) VALUES

(100),

(200),

(300);

select * from sample_table_int;

-- Change the column type from INTEGER to BIGINT

ALTER TABLE sample_table_int

ALTER COLUMN some_integer TYPE BIGINT;

-- Verify the changes

SELECT * FROM sample_table_int;

-- Case 2: Data Type Change with Using Clause (e.g., VARCHAR to INTEGER)

ALTER TABLE table_name

ALTER COLUMN column_name TYPE INTEGER USING column_name::INTEGER;

-- Create the sample table with a VARCHAR column

CREATE TABLE sample_table_varchar_to_int (

    id SERIAL PRIMARY KEY,

    some_varchar VARCHAR(10)

);

-- Insert sample data into the table

INSERT INTO sample_table_varchar_to_int (some_varchar) VALUES

('100'),

('200'),

('300');

-- Change the column type from VARCHAR to INTEGER using the USING clause

ALTER TABLE sample_table_varchar_to_int

ALTER COLUMN some_varchar TYPE INTEGER USING some_varchar::INTEGER;

-- Verify the changes

SELECT * FROM sample_table_varchar_to_int;

-- Case 3: Data Type Change with Complex Transformation

--Add a New Temporary Column:

ALTER TABLE table_name ADD COLUMN new_column_name NEW_DATA_TYPE;

--Update the New Column with Transformed Data:

UPDATE table_name SET new_column_name = transformation_function(old_column_name);

--Drop the Old Column:

ALTER TABLE table_name DROP COLUMN old_column_name;

--Rename the New Column:

ALTER TABLE table_name RENAME COLUMN new_column_name TO old_column_name;

--Example: Changing VARCHAR to DATE

-- Create the sample table with a VARCHAR column

CREATE TABLE sample_table (

    id SERIAL PRIMARY KEY,

    old_varchar_date VARCHAR(10)

);

-- Insert sample data into the table

INSERT INTO sample_table (old_varchar_date) VALUES

('2023-01-01'),

('2023-02-15'),

('2023-03-20');

select * from sample_table;

-- Add a new temporary column with the desired data type

ALTER TABLE sample_table ADD COLUMN new_date_column DATE;

-- Update the new column with transformed data from the old column

UPDATE sample_table SET new_date_column = to_date(old_varchar_date, 'YYYY-MM-DD');

-- Drop the old column

ALTER TABLE sample_table DROP COLUMN old_varchar_date;

-- Rename the new column to the old column’s name

ALTER TABLE sample_table RENAME COLUMN new_date_column TO old_varchar_date;

-- Verify the changes

SELECT * FROM sample_table;

--Remember to build indexes on new column if there was index existing to get optimized performance