Updating Data Using Views in SQL – Complete Guide with Examples

Introduction

In SQL, text data types are used to store alphanumeric values like names, addresses, emails, and descriptions. Choosing the correct text type — CHAR, VARCHAR, or TEXT — is important for optimizing storage space, query speed, and database performance.

In this section, you'll learn the definitions, differences, and best use cases for each text data type.

1. CHAR (Fixed-Length String)

CHAR is used to store fixed-length strings. If the stored string is shorter than the defined length, SQL automatically pads it with spaces to match the specified size.

Features:

• Fixed length
• Fast and predictable performance
• Uses extra storage if the data is often shorter than the specified length

Syntax:

column_name CHAR(length);

length = number of characters (1 to 255 depending on the database system)

Example:

CREATE TABLE countries (
country_code CHAR(2),
country_name CHAR(50)
    );

country_code like 'US', 'IN', 'UK' will always take 2 characters.

When to Use CHAR:

• Data with a constant size, such as country codes, gender ('M', 'F'), state abbreviations
• Fixed-format fields like credit card types ('VISA', 'MC')
• When exact storage size is known and consistent

2. VARCHAR (Variable-Length String)

VARCHAR stands for Variable Character. It stores variable-length strings, meaning only the actual characters are stored without unnecessary padding.

Features:

• Variable length
• More space-efficient than CHAR for varying-length text
• Slightly slower than CHAR when processing large volumes (because of extra calculations for string lengths)

Syntax:

column_name VARCHAR(length);

length = maximum number of characters allowed

Example:

CREATE TABLE employees (
first_name VARCHAR(50),
email VARCHAR(100)
    );

Names and emails can vary in length, making VARCHAR ideal.

When to Use VARCHAR:

• Data with unpredictable or variable length
• Names, emails, addresses, and descriptions under 255-65535 characters
• Most general-purpose text fields

3. TEXT (Large Text Field)

TEXT is used to store large amounts of text like long descriptions, blog posts, comments, or articles.

Features:

• Meant for large text storage (up to 65,535 characters for standard TEXT in MySQL)
• Cannot have a default value (in some databases like MySQL)
• TEXT fields are stored outside the main table with a pointer reference
• Different variants exist (TINYTEXT, MEDIUMTEXT, LONGTEXT) for various sizes

Syntax:

column_name TEXT;

Example:

CREATE TABLE articles (
id INT,
title VARCHAR(255),
body TEXT
   );

body will store the full article content, which can be very large.

When to Use TEXT:

• Long-form text fields (comments, articles, reviews, reports)
• Data that exceeds normal VARCHAR limits
• When exact storage requirements are unknown or potentially very large

Quick Comparison: CHAR vs VARCHAR vs TEXT

Important Tips

• Use CHAR only when all values will be exactly the same length
• VARCHAR is the best choice for most standard text fields
• Reserve TEXT for content that exceeds VARCHAR limits
• Consider VARCHAR(MAX) in SQL Server for large text that might need indexing
• Be aware that TEXT fields may have limitations on default values and full-text indexing

Can You Update Data Through a View?

Yes — some views in SQL are updatable, which means you can run UPDATE, INSERT, or DELETE on them as if they were actual tables. However, not all views support data modification.

When Can a View Be Updated?

A view can be updated if:

• It references a single base table
• It does not use GROUP BY, DISTINCT, HAVING, UNION
• It does not use aggregate functions (like SUM, AVG)
• It does not use LIMIT or OFFSET

A view cannot be updated if:

• It combines multiple tables
• It contains aggregations, joins, or derived values
• It uses set operations or subqueries

Example: Updating Data Through a Simple View

Step 1: Create a View

CREATE VIEW employee_basic AS
SELECT id, name, salary
FROM employees;

Step 2: Update Through the View

UPDATE employee_basic
SET salary = salary + 1000
WHERE id = 101;

This will successfully update the base table employees because the view is simple and direct.

Example: View That Cannot Be Updated

CREATE VIEW high_salary_employees AS
SELECT id, name, salary
FROM employees
WHERE salary > 70000;

Now try:

UPDATE high_salary_employees
SET salary = 75000
WHERE id = 103;

This might fail or behave unexpectedly, depending on your DBMS, because it has a WHERE filter — which could make the result non-deterministic.

Best Practices for Updating Through Views

• Use simple views when you plan to modify data
• Ensure the view maps directly to one table
• Always test your updates to avoid unintended data loss
• Use INSTEAD OF triggers if your DBMS supports them (e.g., in SQL Server or PostgreSQL) to allow controlled updates on complex views

Updating Using Views in PostgreSQL (with Rules/Triggers)

If you're using PostgreSQL, you can define INSTEAD OF triggers to make even complex views updatable.

CREATE OR REPLACE VIEW editable_view AS
SELECT id, name FROM employees;

CREATE RULE update_editable_view AS
ON UPDATE TO editable_view DO INSTEAD
UPDATE employees SET name = NEW.name WHERE id = OLD.id;