Gain insights into fundamental database concepts, relational databases, and entity-relationship diagrams. Learn about normalization techniques and basics of SQL to enhance database efficiency.

Databases are universal - they underlie the technology you use every day. They're a crucial component of everything from telecommunications systems, banking systems, and video games to just about any other software system that maintains some amount of persistent data.

In this course, you'll learn about the fundamental concepts of databases, why and when they're used, what relational databases are, and entity-relationship diagrams. You will also be exposed to techniques like normalization that help to increase the efficiency of databases. You'll wrap up with a look at the basics of Structured Query Language (SQL). 

After completing this course, you will be able to move onto more advanced courses involving database systems and SQL.

Database Design Fundamentals for Software Engineers

# Aggregate functions in SQL

In database management, an aggregate function is a function where the values of multiple rows are grouped together to form a single value of more significant meaning.

We will discuss the following in this lesson:

* `COUNT()`
* `SUM()`
* `AVG()`
* `MIN()`
* `MAX()`

Again we will be using the CUSTOMERS table. 


## The COUNT function

The `COUNT()` function returns the number of rows that match a specified criterion.

### Syntax

The syntax for the `COUNT()` function is as follows:

```sql
SELECT COUNT(column_name)

FROM table_name

WHERE condition;
```

This query will return the number of `Non-Null` values in the specified column.

### Example

Let's say we apply the COUNT function to the `salary` column:





In this lesson, we will learn about the different aggregate functions available in SQL.

Introduction

Fundamental Concepts

Data Modeling

Entity-Relationship Data Model

The Relational Data Model

Functional Dependencies

Normalization

Structured Query Language

Conclusion

Aggregate Functions in SQL

Aggregate functions in SQL

The COUNT function

Syntax