Current File : //opt/alt/postgresql11/usr/share/doc/alt-postgresql11-9.2.24/html/tutorial-concepts.html
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<HTML
><HEAD
><TITLE
>Concepts</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK
REV="MADE"
HREF="mailto:pgsql-docs@postgresql.org"><LINK
REL="HOME"
TITLE="PostgreSQL 9.2.24 Documentation"
HREF="index.html"><LINK
REL="UP"
TITLE="The SQL Language"
HREF="tutorial-sql.html"><LINK
REL="PREVIOUS"
TITLE="Introduction"
HREF="tutorial-sql-intro.html"><LINK
REL="NEXT"
TITLE="Creating a New Table"
HREF="tutorial-table.html"><LINK
REL="STYLESHEET"
TYPE="text/css"
HREF="stylesheet.css"><META
HTTP-EQUIV="Content-Type"
CONTENT="text/html; charset=ISO-8859-1"><META
NAME="creation"
CONTENT="2017-11-06T22:43:11"></HEAD
><BODY
CLASS="SECT1"
><DIV
CLASS="NAVHEADER"
><TABLE
SUMMARY="Header navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="5"
ALIGN="center"
VALIGN="bottom"
><A
HREF="index.html"
>PostgreSQL 9.2.24 Documentation</A
></TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="top"
><A
TITLE="Introduction"
HREF="tutorial-sql-intro.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="top"
><A
HREF="tutorial-sql.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="60%"
ALIGN="center"
VALIGN="bottom"
>Chapter 2. The <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> Language</TD
><TD
WIDTH="20%"
ALIGN="right"
VALIGN="top"
><A
TITLE="Creating a New Table"
HREF="tutorial-table.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="TUTORIAL-CONCEPTS"
>2.2. Concepts</A
></H1
><P
>
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> is a <I
CLASS="FIRSTTERM"
>relational
database management system</I
> (<ACRONYM
CLASS="ACRONYM"
>RDBMS</ACRONYM
>).
That means it is a system for managing data stored in
<I
CLASS="FIRSTTERM"
>relations</I
>. Relation is essentially a
mathematical term for <I
CLASS="FIRSTTERM"
>table</I
>. 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
>
Each table is a named collection of <I
CLASS="FIRSTTERM"
>rows</I
>.
Each row of a given table has the same set of named
<I
CLASS="FIRSTTERM"
>columns</I
>,
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
>
Tables are grouped into databases, and a collection of databases
managed by a single <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> server
instance constitutes a database <I
CLASS="FIRSTTERM"
>cluster</I
>.
</P
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
SUMMARY="Footer navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="tutorial-sql-intro.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="index.html"
ACCESSKEY="H"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="tutorial-table.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Introduction</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="tutorial-sql.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>Creating a New Table</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>
Mini Shell