Sql Excel : NoSQL and Other Types of Databases

NoSQL refers to a type of database that, at first sight, might seem to be the
antithesis of SQL. Actually, the “No” stands for “Not Only.” This terminology can
be used to refer to a variety of different database technologies:
Key-value pairs, where the columns of data can vary between rows—and, quite
importantly—the columns themselves can contain lists of things
Graph-based databases, which specialize in representing and handling
problems from graph theory
Document databases, which are used for analyzing documents and other texts
Geographic information systems (GIS), which are used for geographic analysis
These types of databases are often specialized for particular functions. For
instance, key-value pair databases provide excellent performance in a web
environment for managing data about online sessions.
These technologies are really complementary technologies to traditional relational
databases rather than replacement technologies. For instance, key-value
databases are often used on a website in conjunction with relational databases
that store history. Graph and document databases are often used in conjunction
with data warehouses that support more structured information.
Further, good ideas are not limited to a single technology. One of the motivations
for writing a second edition of this book is that database technology is improving.
SQL and the underlying relational database technology increasingly support
functionality similar to NoSQL databases. For example, recursive common table
expressions provide functionality for traversing graphs. Full text indexes provide
functionality for working with text. Most databases offer extensions for geographic
data. And, increasingly databases are providing better functionality for nested
tables and portable data formats, such as XML and JSON.