How to begin work with Postgres for a new user. Some of the steps required to use Postgres can be performed by any Postgres user, and some must be done by the site database administrator. This site administrator is the person who installed the software, created the database directories and started the postmaster process. This person does not have to be the Unix superuser ("root") or the computer system administrator; a person can install and use Postgres without any special accounts or privileges. If you are installing Postgres yourself, then refer to the Administrator's Guide for instructions on installation, and return to this guide when the installation is complete. Throughout this manual, any examples that begin with the character "%" are commands that should be typed at the Unix shell prompt. Examples that begin with the character "*" are commands in the Postgres query language, Postgres SQL. This section discusses how to set up your own environment so that you can use frontend applications. We assume Postgres has already been successfully installed and started; refer to the Administrator's Guide and the installation notes for how to install Postgres. Postgres is a client/server application. As a user, you only need access to the client portions of the installation (an example of a client application is the interactive monitor psql). For simplicity, we will assume that Postgres has been installed in the directory /usr/local/pgsql. Therefore, wherever you see the directory /usr/local/pgsql you should substitute the name of the directory where Postgres is actually installed. All Postgres commands are installed in the directory /usr/local/pgsql/bin. Therefore, you should add this directory to your shell command path. If you use a variant of the Berkeley C shell, such as csh or tcsh, you would add % set path = ( /usr/local/pgsql/bin path ) in the .login file in your home directory. If you use a variant of the Bourne shell, such as sh, ksh, or bash, then you would add % PATH=/usr/local/pgsql/bin:$PATH % export PATH to the .profile file in your home directory. From now on, we will assume that you have added the Postgres bin directory to your path. In addition, we will make frequent reference to setting a shell variable or setting an environment variable throughout this document. If you did not fully understand the last paragraph on modifying your search path, you should consult the Unix manual pages that describe your shell before going any further. If your site administrator has not set things up in the default way, you may have some more work to do. For example, if the database server machine is a remote machine, you will need to set the PGHOST environment variable to the name of the database server machine. The environment variable PGPORT may also have to be set. The bottom line is this: if you try to start an application program and it complains that it cannot connect to the postmaster, you should immediately consult your site administrator to make sure that your environment is properly set up. Assuming that your site administrator has properly started the postmaster process and authorized you to use the database, you (as a user) may begin to start up applications. As previously mentioned, you should add /usr/local/pgsql/bin to your shell search path. In most cases, this is all you should have to do in terms of preparation. Two different styles of connections are supported. The site administrator will have chosen to allow TCP/IP network connections or will have restricted database access to local (same-machine) socket connections only. These choices become significant if you encounter problems in connecting to a database, since you will want to confirm that you are choosing an allowed connection option. If you get the following error message from a Postgres command (such as psql or createdb): % psql template1 Connection to database 'postgres' failed. connectDB() failed: Is the postmaster running and accepting connections at 'UNIX Socket' on port '5432'? or % psql -h localhost template1 Connection to database 'postgres' failed. connectDB() failed: Is the postmaster running and accepting TCP/IP (with -i) connections at 'localhost' on port '5432'? it is usually because the postmaster is not running, or you are attempting to connect to the wrong server host. If you get the following error message: FATAL 1:Feb 17 23:19:55:process userid (2360) != database owner (268) it means that the site administrator started the postmaster as the wrong user. Tell him to restart it as the Postgres superuser. Now that Postgres is up and running we can create some databases to experiment with. Here, we describe the basic commands for managing a database. Most Postgres applications assume that the database name, if not specified, is the same as the name on your computer account. If your database administrator has set up your account without database creation privileges, then she should have told you what the name of your database is. If this is the case, then you can skip the sections on creating and destroying databases. Let's say you want to create a database named mydb. You can do this with the following command: % createdb mydb If you do not have the privileges required to create a database, you will see the following: % createdb mydb WARN:user "your username" is not allowed to create/destroy databases createdb: database creation failed on mydb. Postgres 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. Not every user has authorization to become a database administrator. If Postgres refuses to create databases for you, then the site administrator needs to grant you permission to create databases. Consult your site administrator if this occurs. Once you have constructed a database, you can access it by: Running the Postgres terminal monitor programs (e.g. psql) which allows you to interactively enter, edit, and execute SQL commands. Using an existing native frontend tool like pgaccess or ApplixWare (via ODBC) to create and manipulate a database. Using a language like perl or tcl which has a supported interface for Postgres. Some of these languages also have convenient and powerful GUI toolkits which can help you construct custom applications. pgaccess, mentioned above, is one such application written in tk/tcl and can be used as an example. Writing a C program using the LIBPQ subroutine library. This allows you to submit SQL commands from C and get answers and status messages back to your program. This interface is discussed further in The PostgreSQL Programmer's Guide. You might want to start up psql, to try out the examples in this manual. It can be activated for the mydb database by typing the command: % psql mydb You will be greeted with the following message: 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=> This prompt indicates that the terminal monitor is listening to you and that you can type SQL queries into a workspace maintained by the terminal monitor. The psql program responds to escape codes that begin with the backslash character, "\" For example, you can get help on the syntax of various Postgres SQL commands by typing: mydb=> \h Once you have finished entering your queries into the workspace, you can pass the contents of the workspace to the Postgres server by typing: mydb=> \g This tells the server to process the query. If you terminate your query with a semicolon, the "\g" is not necessary. psql will automatically process semicolon terminated queries. To read queries from a file, say myFile, instead of entering them interactively, type: mydb=> \i fileName To get out of psql and return to Unix, type mydb=> \q and psql will quit and return you to your command shell. (For more escape codes, type \h at the monitor prompt.) White space (i.e., spaces, tabs and newlines) may be used freely in SQL queries. Single-line comments are denoted by "--". Everything after the dashes up to the end of the line is ignored. Multiple-line comments, and comments within a line, are denoted by "/* ... */". If you are the database administrator for the database mydb, you can destroy it using the following Unix command: % dropdb mydb 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.