<Chapter>
<Title>Managing a Database</Title>

<Para>
<Note>
<Para>
This section is currently a thinly disguised copy of the Tutorial. Needs to be augmented.
- thomas 1998-01-12
</Para>
</Note>
</Para>

<Para>
Although the <FirstTerm>site administrator</FirstTerm> is responsible for overall management of the
<ProductName>Postgres</ProductName> installation, some databases within the
installation may be managed by another person, designated the <FirstTerm>database administrator</FirstTerm>.
This assignment of responsibilities occurs when a database is created. A user may be assigned
explicit privileges to create databases and/or to create new users. A user assigned both privileges
can perform most administrative task within <ProductName>Postgres</ProductName>, but will
not by default have the same operating system privileges as the site administrator.
</Para>

<Para>
The Database Administrator's Guide covers these topics in more detail.
</Para>

<Sect1>
<Title>Database Creation</Title>

<Para>
Databases are created by the <Command>create database</Command> issued from
within <ProductName>Postgres</ProductName>. <Application>createdb</Application> is a command-line
utility provided to give the same functionality from outside <ProductName>Postgres</ProductName>.
</Para>

<Para>
The <ProductName>Postgres</ProductName> backend must be running for either method
to succeed, and the user issuing the command must be the <ProductName>Postgres</ProductName>
<FirstTerm>superuser</FirstTerm> or have been assigned database creation privileges by the
superuser.
</Para>

<Para>
To create a new database named <Quote>mydb</Quote> from the command line, type
<ProgramListing>
% createdb mydb
</ProgramListing>

and to do the same from within <Application>psql</Application> type
<ProgramListing>
* CREATE DATABASE mydb;
</ProgramListing>
</Para>

<Para>
If you do not have the privileges required to create a database, you will see
the following:
<ProgramListing>
% createdb mydb
WARN:user "your username" is not allowed to create/destroy databases
createdb: database creation failed on mydb.
</ProgramListing>
</Para>

<Para>
<ProductName>Postgres</ProductName>  allows  you to create any number of databases
at a  given  site  and  you  automatically  become  the
database  administrator  of  the database you just created.  
Database names must  have  an  alphabetic  first
character and are limited to 32 characters in length.
</Para>

</Sect1>

<Sect1>
<Title>Alternate Database Locations</Title>

<Para>
It is possible to create a database in a location other than the default
location for the installation. Remember that all database access actually
occurs through the database backend, so that any location specified must
be accessible by the backend.

<Para>
 Either an absolute path name or an environment variable
may be specified as a location.
Any environment variable specifying an alternate location must have
been defined before the backend was started.
Consult with the site administrator
regarding preconfigured alternate database locations.

<Note>
<Para>
 The environment variable style of specification
is to be preferred since it allows the site administrator more flexibility in
managing disk storage.
</Para>
</Note>

<Para>
For security and integrity reasons,
any path or environment variable specified has some
additional path fields appended.

<Para>
Alternate database locations must be prepared by running <Application>initlocation</Application>.

<Para>
To create a data storage area in <FileName>/alt/postgres/data</FileName>, ensure
that <FileName>/alt/postgres</FileName> already exists.
From the command line, type
<ProgramListing>
% initlocation /alt/postgres/data
Creating Postgres database system directory /alt/postgres/data

Creating Postgres database system directory /alt/postgres/data/base

</ProgramListing>

<Para>
To do the same using an environment variable PGDATA2, type
<ProgramListing>
% initlocation $PGDATA2
Creating Postgres database system directory /alt/postgres/data

Creating Postgres database system directory /alt/postgres/data/base

</ProgramListing>

<Para>
To create a database in the alternate storage area <FileName>/alt/postgres/data</FileName>
from the command line,
type
<ProgramListing>
% createdb -D /alt/postgres/data mydb
</ProgramListing>

or

<ProgramListing>
% createdb -D PGDATA2 mydb
</ProgramListing>

and to do the same from within <Application>psql</Application> type
<ProgramListing>
* CREATE DATABASE mydb WITH LOCATION = 'PGDATA2';
</ProgramListing>
</Para>

<Para>
If you do not have the privileges required to create a database, you will see
the following:
<ProgramListing>
% createdb mydb
WARN:user "your username" is not allowed to create/destroy databases
createdb: database creation failed on mydb.
</ProgramListing>
</Para>

<Para>
If the specified location does not exist or the database backend does not have
permission to access it or to write to directories under it, you will see
the following:
<ProgramListing>
% createdb -D /alt/postgres/data mydb
ERROR:  Unable to create database directory /alt/postgres/data/base/mydb
createdb: database creation failed on mydb.
</ProgramListing>

</Sect1>

<Sect1>
<Title>Accessing a Database</Title>

<Para>
     Once you have constructed a database, you can access it
     by:

<ItemizedList Mark="bullet" Spacing="compact">
<ListItem>
<Para>
running the <ProductName>Postgres</ProductName>  terminal  monitor  programs  (e.g.
        <Application>psql</Application>) which allows you to interactively
        enter, edit, and execute <Acronym>SQL</Acronym> commands.
</Para>
</ListItem>
<ListItem>
<Para>
      writing a  C  program  using  the  LIBPQ  subroutine
        library.   This  allows  you  to submit <Acronym>SQL</Acronym> commands
        from C and get answers and status messages  back  to
        your  program.   This interface is discussed further
        in section ??.
</Para>
</ListItem>
</ItemizedList>

You might want to start up <Application>psql</Application>, to try out the examples in this manual.
 It can be activated for the <Database>mydb</Database>
     database by typing the command:
<ProgramListing>
% psql mydb
</ProgramListing>

     You will be greeted with the following message:
<ProgramListing>
Welcome to the POSTGRESQL interactive sql monitor:
  Please read the file COPYRIGHT for copyright terms of POSTGRESQL

   type \? for help on slash commands
   type \q to quit
   type \g or terminate with semicolon to execute query
 You are currently connected to the database: template1

mydb=>
</ProgramListing>
</Para>

<Para>
This prompt indicates that the terminal monitor is listening
  to you and that you can type <Acronym>SQL</Acronym> queries into a
     workspace maintained by the terminal monitor.
     The <Application>psql</Application> program responds to escape  codes  that  begin
     with  the  backslash  character, <Quote>\</Quote>  For example, you
     can get help on the syntax of various
 <ProductName>Postgres</ProductName> <Acronym>SQL</Acronym> commands by typing:
<ProgramListing>
mydb=> \h
</ProgramListing>

     Once  you  have finished entering your queries into the
     workspace, you can pass the contents of  the  workspace
     to the <ProductName>Postgres</ProductName> server by typing:
<ProgramListing>
mydb=> \g
</ProgramListing>

     This  tells  the  server  to process the query.  If you
     terminate your query with a semicolon, the  <Quote>\g</Quote> is  not
     necessary.   <Application>psql</Application> will automatically process semicolon terminated queries.
     To read queries from a file,  say  myFile,  instead  of
     entering them interactively, type:
<ProgramListing>
mydb=> \i fileName
</ProgramListing>

     To get out of <Application>psql</Application> and return to UNIX, type
<ProgramListing>
mydb=> \q
</ProgramListing>

     and  <Application>psql</Application>  will  quit  and  return  you to your command
     shell. (For more escape codes, type <Command>\h</Command> at  the  monitor
     prompt.)
     White  space  (i.e.,  spaces, tabs and newlines) may be
     used freely in <Acronym>SQL</Acronym> queries.  Single-line comments  are  denoted  by
     <Quote>--</Quote>.   Everything  after the dashes up to the end of the
     line is ignored. Multiple-line comments, and comments within a line,
     are denoted by <Quote>/* ... */</Quote>
</Para>

<Sect2>
<Title>Database Privileges</Title>

<Para>
</Sect2>

<Sect2>
<Title>Table Privileges</Title>

<Para>
TBD
</Para>

</Sect2>

</Sect1>
     
<Sect1>
<Title>Destroying a Database</Title>

<Para>
     If you are the database administrator for the  database
     <Database>mydb</Database>,  you can destroy it using the following UNIX command:
<ProgramListing>
% destroydb mydb
</ProgramListing>
     This action physically removes all of  the  UNIX  files
     associated  with  the database and cannot be undone, so
     this should only be done with a  great  deal  of  forethought.
</Para>
</Sect1>

</Chapter>
