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 AND & OR clauses

The SQL **AND & OR** operators are used to combine multiple conditions in order to narrow data in an SQL statement. These two operators are called the **conjunctive operators**.

These operators provide a means to make multiple comparisons with different operators in the same SQL statement.

## The AND Operator

The `AND` operator allows the existence of multiple conditions in a SQL statement's `WHERE` clause.

### Syntax

The basic syntax of the `AND` operator with a `WHERE` clause is as follows:

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

FROM table_name

WHERE [condition1] AND [condition2]...AND [conditionN];
```

You can combine N number of conditions using the `AND` operator. For an action to be taken by the SQL statement, whether it be a transaction or a query, all conditions separated by the `AND` must be `TRUE`.

### Example

In this example, we will retrieve the `ID`, `Name` and `Salary` fields from the CUSTOMERS table, where the salary is greater than $20,000 (inclusive) and the age is less than 25 years.

The steps needed to solve this problem are highlighted below:



# The AND & OR clauses

The SQL **AND & OR** operators are used to combine multiple conditions in order to narrow data in an SQL statement. These two operators are called the **conjunctive operators**.

These operators provide a means to make multiple comparisons with different operators in the same SQL statement.

# The AND Operator

The `AND` operator allows the existence of multiple conditions in a SQL statement's `WHERE` clause.

## Syntax

The basic syntax of the `AND` operator with a `WHERE` clause is as follows:

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

FROM table_name

WHERE [condition1] AND [condition2]...AND [conditionN];
```

You can combine N number of conditions using the `AND` operator. For an action to be taken by the SQL statement, whether it be a transaction or a query, all conditions separated by the `AND` must be `TRUE`.

## Example

In this example, we will retrieve the `ID`, `Name` and `Salary` fields from the CUSTOMERS table, where the salary is greater than $20,000 (inclusive) and the age is less than 25 years.

The steps needed to solve this problem are highlighted below:



In this lesson, we will discuss how can we combine multiple conditions in WHERE using the AND & OR operators.

Introduction

Fundamental Concepts

Data Modeling

Entity-Relationship Data Model

The Relational Data Model

Functional Dependencies

Normalization

Structured Query Language

Conclusion

The AND & OR Clauses

The AND & OR clauses

The AND Operator