**************************
Structure of Data in RDBMS
**************************

The database itself is a set of data stored in a computer. This data is usually
structured in a way that makes them easily accessible. Relational databases
use the structure that allows us to identify and access data in *relation* to
another piece of data in the database.

Understanding the basic structure of an RDBMS is crucial for effectively
managing and querying data. In this section, we delve into the core components:
*tables*, *rows*, and *columns*, and how they form the foundation of
a relational database.

.. contents::
   :local:
   :depth: 2

Tables
======

..  in case updates are required - refer to documentation
    https://www.postgresql.org/docs/current/ddl-basics.html

Tables are the building blocks.

.. note::

    Some documents may name tables as *relations*.

A table in an RDBMS is akin to a spreadsheet. It is where data is stored and
organized. Each table in a database represents a specific entity or concept,
like ``Customers`` or ``Orders``.

Structure and purpose
---------------------

A table consists of rows and columns, similar to a grid. All the rows and cols
together are the data *related* to some subject or concept within a database.

Tables hold data about a particular subject, such as all the information
related to customer transactions, or books available in a local library.

Naming conventions
------------------

.. important::

    The conventions below aren't related to tables only, but also they are
    used when naming databases and columns.

-   Use nouns that describe the subject the best.
-   Use lowercase names, e.g. ``user`` instead of ``Users`` or ``USERS``.
-   If the name must consist of two or more words, use underscore to connect
    them, e.g. ``snake_case``, ``user_account``.
-   Avoid use of dots, spaces, or dashes.
-   When naming objects, balance the objective of keeping names short and easy
    to use with the objective of making names as descriptive as possible.
-   Singular names are preferred over plurals.

Rows: Individual Records
========================

Tables can have hundreds, thousands, sometimes even millions of rows of data.
These rows are offer called *records*. Each row in a table represents a single
entity of a subject. For example, ``book`` table represents an abstract book
with all its attributes, like title, author etc. And a specific row within this
table represents a concrete book.

Every row should ideally have something that make it unique.

Rows in a table can be linked to other rows in other tables or within the same
table, maintaining relationships and data integrity.

Columns: Attributes of Data
===========================

Columns in a table represent the attributes of the entity. For instance,
``book`` table may contain columns ``title``, ``author``, ``publisher`` etc.

Each column has a defined data type, like ``integer``, ``string`` etc.

Constraints
-----------

Columns can have constraints to enforce data integrity. For example, some
columns cannot be empty, or store values under or above some threshold.
Several constraints can be combined together.

Examples
========

.. csv-table:: Authors table
    :header-rows: 1
    :stub-columns: 1

    id,first_name,last_name,country,birthdate
    1,Letta,Casbolt,Poland,1947-04-18
    2,Robbyn,Attwoul,Poland,1954-10-17
    3,Hesther,Kisby,Ukraine,1941-07-21
    4,Gav,Jewett,Czech Republic,1988-02-05
    5,Jorrie,Klehyn,United States,1941-08-07
    6,Genevieve,Ollington,United States,1921-08-27
    7,Carrissa,Arrandale,United Kingdom,1982-08-20
    8,Josepha,Dominichelli,Poland,1976-12-03
    9,Ario,Hepher,Ukraine,2003-10-11
    10,Walker,Grolmann,Poland,1964-02-17