# Basic relational database concepts

Basic relational database concepts

Term | Description | Example
--- | --- | ---
Tables | Made up of rows and columns. Store collections of related data. | Subjects, Visits, and Forms tables.
Rows | Occurrences (records) of related data values in a database table. Each time you enter new data in a table, you create a row in that table. | Subjects, Visits, and Forms rows.
Columns | Occurrences (records) of individual data values in a database table. | The columns in the Subjects table might store a Subject ID, Subject Number, Subject Initials, Current Status, and First Screened Date for each subject (row) in the study.
Primary keys | Columns in a database table whose values uniquely identify a row in a table. | The Subject ID column in the Subjects table is a primary key because each Subject ID value can only occur one time in that table and is unique to each subject.
Foreign keys | Columns in a database table that establish relationships with other tables in the database. | The Subject ID column in the Visits table is a foreign key that allows you to create a relationship between the Visits table and the Subjects table as well as a relationship between the Visits table and the Forms table.
Joins | Expressions of relationships between database tables. A join occurs when you match the data value of a key (primary or foreign) in one table to the data value of a key in another table to retrieve related data. | To retrieve a visit and form data for a subject: Join the Subject ID value in the Subjects table to the Subject ID value in the Visits table. Join the Subject ID value in the Visits table to the Subject ID value in the Forms table.

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