1. Relational Databases

2. Why Databases As programs get larger, data becomes more important
Data is entities and relationships
Real-world processes involve complex data interaction

3. Structure of a Database
Record – one discreet entity
Field – one piece of data
Table – series of like records

4. Record Represents some entity Consists of many details
All details refer to same record

5. Field Specific data elements Has a name, length, type, value
Sometimes length is assumed
Each record has same field definitions, but different values

6. Table A series of records following the same definition
All records should describe same kind of thing
Each record is a different instance of that thing

7. Database A series of tables each defining different entities
The relationships between those entities
Ancillary files, indices, views

8. Primary Keys
A primary key is a field or group of fields that uniquely identifies a record. A primary key comprised of two or more fields is called a composite primary key. Every table must have a primary key!
The most important key in a table:
Uniquely identifies a specific record throughout a database
Identifies a specific table throughout the database
Enforces table-level integrity
Helps to establish relationships between tables

9. Foreign Keys
A foreign key is important when establishing relationships between tables.
To create a foreign key, you would take a primary key from one table and incorporate it in a second table. In the second table, the key becomes a foreign key.
Foreign keys enforce relationship-level integrity – values in one table's foreign key field must match exactly with the corresponding values of a second table's primary key field.

10. Table Relationships
We categorize table relationships in the Relational Model as follows:
One-to-One (1:1)
One-to-Many (1:N)
Many-to-Many (N:N)
To establish a relationship between tables, we need to match values of a shared field.

11. One-To-One Relationships (1:1)
A record in one table (a parent table) is related to one and only one record in a second table (a child table). A record in a second table (the child table) is related to one and only one record in the first table (the parent table).
We create a 1:1 relationship by copying the primary key of a parent table into a child table, where it becomes a foreign key.
This type of relationship is unique because both tables share the same primary key. The primary key in the child table serves both as that table's primary key and a foreign key .

12. One-To-Many Relationships (1:N)
A record in one table (a parent table) can be related to many records in a second table (a child table). A single record in the child table is related to one and only one record in the parent table.
We create a 1:N relationship by copying the primary key of a parent table into a child table, where it becomes a foreign key.
This type of relationship is the most common type of relationship in the relational database model.

13. Many-To-Many Relationships (N:N)
A record in one table can be related to many records in a second table. A single record in the second table can be related to many records in the parent table.
We create a N:N relationship by copying the primary keys of a each table into a third table, called a linking (associative) table. Together, the copied keys form a composite primary key. Individually, they serve as foreign keys for the other table.

14. Example of N:N Relationship

15. SQL Structured Query Language
Uniform system for defining, querying data
Used by many programming languages and db tools