Once you have constructed a database, you can access it by:
running the Postgres terminal monitor program (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 the PostgreSQL Programmer's Guide.
% psql dbname
You will be greeted with the following message:
Welcome to the Postgres interactive sql monitor:
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: dbname
dbname=>
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:
dbname=> \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:
dbname=> \g
This tells the server to process the query. If you terminate
your query with a semicolon, the backslash-g is not necessary.
psql will automatically process
semicolon terminated queries. To read queries from a file, instead
of entering them interactively, type:
dbname=> \i filename
To get out of psql and
return to UNIX, type
dbname=> \q
and psql will quit and
return you to your command shell. (For more escape codes, type
backslash-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
two dashes (“--”). Everything after the dashes up to the end of the
line is ignored. Multiple-line comments, and comments within a
line, are denoted by “/* ... */”, a convention borrowed from
Ingres.