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- <a id="id-1.4.4.3.2.1" class="indexterm"></a>
- <a id="id-1.4.4.3.2.2" class="indexterm"></a>
- <a id="id-1.4.4.3.2.3" class="indexterm"></a>
- <a id="id-1.4.4.3.2.4" class="indexterm"></a>
- <a id="id-1.4.4.3.2.5" class="indexterm"></a>
-
- <span class="productname">PostgreSQL</span> is a <em class="firstterm">relational
- database management system</em> (<acronym class="acronym">RDBMS</acronym>).
- That means it is a system for managing data stored in
- <em class="firstterm">relations</em>. Relation is essentially a
- mathematical term for <em class="firstterm">table</em>. The notion of
- storing data in tables is so commonplace today that it might
- seem inherently obvious, but there are a number of other ways of
- organizing databases. Files and directories on Unix-like
- operating systems form an example of a hierarchical database. A
- more modern development is the object-oriented database.
- </p><p>
- <a id="id-1.4.4.3.3.1" class="indexterm"></a>
- <a id="id-1.4.4.3.3.2" class="indexterm"></a>
-
- Each table is a named collection of <em class="firstterm">rows</em>.
- Each row of a given table has the same set of named
- <em class="firstterm">columns</em>,
- and each column is of a specific data type. Whereas columns have
- a fixed order in each row, it is important to remember that SQL
- does not guarantee the order of the rows within the table in any
- way (although they can be explicitly sorted for display).
- </p><p>
- <a id="id-1.4.4.3.4.1" class="indexterm"></a>
- <a id="id-1.4.4.3.4.2" class="indexterm"></a>
-
- Tables are grouped into databases, and a collection of databases
- managed by a single <span class="productname">PostgreSQL</span> server
- instance constitutes a database <em class="firstterm">cluster</em>.
- </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="tutorial-sql-intro.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="tutorial-sql.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="tutorial-table.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">2.1. Introduction </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 2.3. Creating a New Table</td></tr></table></div></body></html>
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