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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 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 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
PostgreSQLSQL 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 "/* ... */".
