#### Schemas and Relationships  --- #### What is a database relationship? :sparkles: A relationship is established between two database tables when one table uses a foreign key that references the primary key of another table. :key: ---> :key: --- #### Why is it important :question: Establishing consistent relationships between database tables helps ensure data integrity, contributing to database normalization. --- #### What kinds of database relationships are there? - one to one. - one to many. - many to many. --- #### How does a schema describe a relational database? - A database schema is a design that represents the storage of your data in a database. - It describes both the organization of data and the relationships between tables in a given database. --- - A database schema is a blueprint of how our data will look. It doesn’t hold data itself, but instead describes the shape of the data and how it might relate to other tables or models. - Logical Vs Physical. ---  --- #### Keys :key: Databases have a few different types of keys --- #### Candidate key - Uniquely identifies a database entry without referring to any other data - Does not describe any relationships to other tables - Each table may have one or more candidate keys --- For example, a company might use Social Security numbers as a candidate key to uniquely identify employees  --- Some people share the same first names, last names, and position, but no two people use the same Social Security number --- Among the candidate keys, one is selected as the table primary key. A table can contain several candidate keys, but only one primary key.  --- #### Primary key Usually the first column in a table and can be automatically generated by the database  --- #### Foreign key A foreign key is another candidate key (not the primary key) used to link an entry to data in another table --- Here, the Courses table primary key is Course_ID. The foreign key is Teacher_ID  --- The foreign key establishes a relationship between the Teachers and Courses tables :handshake:  --- ...and they live happily ever after in a well organised database!