INNER JOIN in SQL – A 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

What is an INNER JOIN?

An INNER JOIN in SQL is used to retrieve only the matching records from two or more tables based on a related column (usually a primary key in one table and a foreign key in the other).

If a record in either table does not have a match, it will not appear in the result.

Syntax of INNER JOIN

SELECT table1.column1, table2.column2, ...
FROM table1
INNER JOIN table2
ON table1.common_column = table2.common_column;

table1 and table2: The tables you're joining

common_column: The column they share (used to relate the records)

Real-Life Example

Tables:

employees

departments

Query:

SELECT 
  employees.name, 
  departments.department_name
FROM employees
INNER JOIN departments
ON employees.department_id = departments.id;

Result:

Charlie is not included because he has no department (NULL value).

When to Use INNER JOIN

• When you want only related data from two tables
• When you're sure the relationship exists in both tables
• Common in queries involving foreign keys (e.g., customer orders, employee departments)

INNER JOIN with Aliases

You can simplify your SQL using aliases:

SELECT e.name, d.department_name
FROM employees e
INNER JOIN departments d
ON e.department_id = d.id;

INNER JOIN with Multiple Tables

You can join more than two tables in a single query:

SELECT o.order_id, c.name, p.product_name
FROM orders o
INNER JOIN customers c ON o.customer_id = c.id
INNER JOIN products p ON o.product_id = p.id;

This retrieves orders with both customer and product details.

Key Points

• Only rows with matching values in both tables are returned.
• It's the most commonly used JOIN in SQL.
• It helps normalize and combine related data efficiently.