Combining GROUP BY with Aggregate Functions in SQL

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

Why Combine GROUP BY with Aggregates?

The GROUP BY clause works together with aggregate functions to summarize data in meaningful ways.

It lets you organize rows into groups and then calculate summary values per group — such as totals, averages, counts, etc.

Common Aggregate Functions Used with GROUP BY

Syntax

SELECT column_name, AGGREGATE_FUNCTION(column_name)
FROM table_name
GROUP BY column_name;

Example Table: orders

Example 1: Total Amount Spent by Each Customer

SELECT customer_id, SUM(amount) AS total_spent
FROM orders
GROUP BY customer_id;

Result:

Example 2: Average Order Amount per Customer

SELECT customer_id, AVG(amount) AS avg_order
FROM orders
GROUP BY customer_id;

Example 3: Number of Orders per Customer

SELECT customer_id, COUNT(order_id) AS order_count
FROM orders
GROUP BY customer_id;

Example 4: Highest Order Amount per Customer

SELECT customer_id, MAX(amount) AS highest_order
FROM orders
GROUP BY customer_id;

Combining Multiple Aggregates

You can include multiple aggregate functions in one query:

SELECT 
  customer_id, 
  COUNT(*) AS total_orders, 
  SUM(amount) AS total_spent, 
  AVG(amount) AS avg_spent
FROM orders
GROUP BY customer_id;

Best Practices

• Always include in GROUP BY any column that is not aggregated.
• Use meaningful aliases for aggregated columns (AS total, AS count, etc.)
• Combine with ORDER BY to sort summarized results.
• Use HAVING to filter aggregated data if needed.

Real-World Use Cases

• Sales totals per product, region, or sales rep
• Average ratings per user or item
• Count of transactions per customer
• Highest or lowest scores per test or student