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

# The HAVING clause

The **HAVING** clause is utilized in SQL as a conditional clause with the `GROUP BY` clause. This conditional clause only returns rows where aggregate function results are matched with given conditions. 

The `HAVING` clause was added to SQL because the `WHERE` keyword could not be used with aggregate functions.

## Syntax

The basic syntax of the `HAVING` clause is as follows:

```sql
SELECT column1, column2, ... columnN

FROM table_name

WHERE [ conditions ]

GROUP BY column1, column2, ... columnN

HAVING [ conditions ]

ORDER BY column1, column2, ... columnN;
```

As you can see, the `HAVING` clause must follow the `GROUP BY` clause in a query and must also precede the `ORDER BY` clause if used.

## Example

Consider the CUSTOMERS table below but with a few changes:

|  ID   |  NAME   | AGE    |  ADDRESS   |  SALARY   |
| --- | --- | --- | --- | --- |
|  1   | Mark    |  32   |  Texas   |  50,000  |
|  2   | Jeff   |  23   |  LA   |  77,000   |
|  3   | John    |  25   |  NY   | 65,000  |
|  4   | Emily    |  23   |  Ohio   | 20,000  |
|  5   | John    |  31   | Texas   | 54,000    |
|  6   | Bill    |  25   | Texas  | 75,000   |
|  7   | Bob    |  28   |  NY   |  31,000   |
|  8   | Elyse   |  29   | Ohio   |  43,000   |
|  9  |  Tom   |   27   | Washington | 35,000  |
|  10   |  Jane   | 22    | NY  |  45,0000 |


As you can see, there are many customers that live at the same `ADDRESS` (i.e. live in the same state).

We want to write a SQL statement that returns the number of customers in each state, but only if that state has more than 2 customers:

In this lesson, we will learn about the HAVING clause.

Introduction

Fundamental Concepts

Data Modeling

Entity-Relationship Data Model

The Relational Data Model

Functional Dependencies

Normalization

Structured Query Language

Conclusion

The HAVING Clause

The HAVING clause

Syntax