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Module C Preface
================

A lot of the data that we interact with today is stored in databases. You can
think of a database as a group of tables. These tables have rows and columns
just like spreadsheets. Some examples of data that can be stored in databases
are listed below.

-   Student records, including grades, at a school
-   Posts and friends in your favorite social network
-   News stories on a newspaper’s website
-   Your contacts list on your mobile phone
-   All images that make up Google Maps

All these bits of information are stored in various kinds of databases. Some of
these are stored in a relational database, which is a database that stores data
points that are related to one another in some way. These databases are
available as open source tools like Postgresql, MySQL and SQLite, as well as
commercial databases such as `Google BigQuery`_, `Oracle`_,
`Microsoft SQL Server`_, or `Amazon Aurora`_. Others are stored in proprietary
systems like Google’s `BigTable`_ or Facebook’s `Haystack Object Store`_.

While the mechanism and content of the database may vary, there is a
common language used to extract data: this language is called Structured Query
Language (SQL, pronounced “sequel”). This module will teach you how you can use
SQL to analyze data in a database.


.. _Google BigQuery: https://cloud.google.com/bigquery/
.. _Oracle: https://www.oracle.com/database/technologies/
.. _Microsoft SQL Server: https://azure.microsoft.com/en-us/services/virtual-machines/sql-server/
.. _Amazon Aurora: https://aws.amazon.com/rds/aurora/
.. _BigTable: https://en.wikipedia.org/wiki/Bigtable
.. _Haystack Object Store: https://code.fb.com/core-data/needle-in-a-haystack-efficient-storage-of-billions-of-photos/