1.4. Accessing a Database

1.4. Accessing a Database
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+ Once you have created a database, you can access it by: + +

+ Running the PostgreSQL interactive + terminal program, called psql, which allows you + to interactively enter, edit, and execute + SQL commands. +
+ Using an existing graphical frontend tool like + pgAdmin or an office suite with + ODBC or JDBC support to create and manipulate a + database. These possibilities are not covered in this + tutorial. +
+ Writing a custom application, using one of the several + available language bindings. These possibilities are discussed + further in Part IV. +

+ + You probably want to start up psql to try + the examples in this tutorial. It can be activated for the + mydb database by typing the command: +

+$ psql mydb
+

+ If you do not supply the database name then it will default to your + user account name. You already discovered this scheme in the + previous section using createdb. +

+ In psql, you will be greeted with the following + message: +

+psql (13.4)
+Type "help" for help.
+
+mydb=>
+

+ + The last line could also be: +

+mydb=#
+

+ That would mean you are a database superuser, which is most likely + the case if you installed the PostgreSQL instance + yourself. Being a superuser means that you are not subject to + access controls. For the purposes of this tutorial that is not + important. +

+ If you encounter problems starting psql + then go back to the previous section. The diagnostics of + createdb and psql are + similar, and if the former worked the latter should work as well. +

+ The last line printed out by psql is the + prompt, and it indicates that psql is listening + to you and that you can type SQL queries into a + work space maintained by psql. Try out these + commands: + +

+mydb=> SELECT version();
+                                         version
+------------------------------------------------------------------------------------------
+ PostgreSQL 13.4 on x86_64-pc-linux-gnu, compiled by gcc (Debian 4.9.2-10) 4.9.2, 64-bit
+(1 row)
+
+mydb=> SELECT current_date;
+    date
+------------
+ 2016-01-07
+(1 row)
+
+mydb=> SELECT 2 + 2;
+ ?column?
+----------
+        4
+(1 row)
+

+ The psql program has a number of internal + commands that are not SQL commands. They begin with the backslash + character, “\”. + For example, + you can get help on the syntax of various + PostgreSQL SQL + commands by typing: +

+mydb=> \h
+

+ To get out of psql, type: +

+mydb=> \q
+

+ and psql will quit and return you to your + command shell. (For more internal commands, type + \? at the psql prompt.) The + full capabilities of psql are documented in + psql. In this tutorial we will not use these + features explicitly, but you can use them yourself when it is helpful. +

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1.3. Creating a Database	Home	Chapter 2. The SQL Language