This section is currently a thinly disguised copy of the Tutorial. Needs to be augmented. - thomas 1998-01-12 Although the site administrator is responsible for overall management of the Postgres installation, some databases within the installation may be managed by another person, designated the database administrator. 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 Postgres, but will not by default have the same operating system privileges as the site administrator. The Database Administrator's Guide covers these topics in more detail. Databases are created by the create database issued from within Postgres. createdb is a command-line utility provided to give the same functionality from outside Postgres. The Postgres backend must be running for either method to succeed, and the user issuing the command must be the Postgres superuser or have been assigned database creation privileges by the superuser. To create a new database named mydb from the command line, type % createdb mydb and to do the same from within psql type => CREATE DATABASE mydb; If you do not have the privileges required to create a database, you will see the following: ERROR: CREATE DATABASE: Permission denied. 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. 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. Alternate database locations are created and referenced by an environment variable which gives the absolute path to the intended storage location. This environment variable must have been defined before the backend was started and the location it points to must be writable by the postgres administrator account. Consult with the site administrator regarding preconfigured alternate database locations. Any valid environment variable name may be used to reference an alternate location, although using variable names with a prefix of PGDATA is recommended to avoid confusion and conflict with other variables. In previous versions of Postgres, it was also permissable to use an absolute path name to specify an alternate storage location. Although the environment variable style of specification is to be preferred since it allows the site administrator more flexibility in managing disk storage, it is also possible to use an absolute path to specify an alternate location. The administrator's guide discusses how to enable this feature. For security and integrity reasons, any path or environment variable specified has some additional path fields appended. Alternate database locations must be prepared by running initlocation. To create a data storage area using the environment variable PGDATA2 (for this example set to /alt/postgres), ensure that /alt/postgres already exists and is writable by the Postgres administrator account. Then, from the command line, type % initlocation PGDATA2 Creating Postgres database system directory /alt/postgres/data Creating Postgres database system directory /alt/postgres/data/base To create a database in the alternate storage area PGDATA2 from the command line, use the following command: % createdb -D PGDATA2 mydb and to do the same from within psql type => CREATE DATABASE mydb WITH LOCATION = 'PGDATA2'; If you do not have the privileges required to create a database, you will see the following: ERROR: CREATE DATABASE: permission denied 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: ERROR: The database path '/no/where' is invalid. This may be due to a character that is not allowed or because the chosen path isn't permitted for databases. Once you have constructed a database, you can access it by: running the PostgreSQL interactive terminal psql which allows you to interactively enter, edit, and execute SQL commands. 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 section ??. 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 psql, the PostgreSQL interactive terminal. Type: \copyright for distribution terms \h for help with SQL commands \? for help on internal slash commands \g or terminate with semicolon to execute query \q to quit mydb=> This prompt indicates that psql 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 PostgreSQL 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 \? at the psql 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 /* ... */ TBD If you are the owner of 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.