2013/2/14 Aleksey Tsalolikhin <atsaloli.tech@xxxxxxxxx>:
> Below is an example of feeding query output to gnuplot without leaving psql.
> I'd like to call it as "select graph(select * from example)", just for fun.
> What do I need to learn to do that, please? Can I create a function that
> uses "\o"? I think not, because a function runs server-side and \o is a
> client side feature.
You are correct, it is not possible for a backend function to interact
directly with psql. You'd need to create a function in PL/Perl etc.,
> Below is an example of feeding query output to gnuplot without leaving psql.
> I'd like to call it as "select graph(select * from example)", just for fun.
> What do I need to learn to do that, please? Can I create a function that
> uses "\o"? I think not, because a function runs server-side and \o is a
> client side feature.
You are correct, it is not possible for a backend function to interact
directly with psql. You'd need to create a function in PL/Perl etc.,
and would have to have gnuplot available on the DB server.
What you could do is create a small psql script along these lines:
barwick@localhost:~$ cat tmp/plot.psql
\set QUIET yes
\t\a\f ' '
\unset QUIET
\o | /usr/bin/gnuplot
select 'set title "My Graph"; set terminal dumb 78 24; set key off; set ylabel "Time"; set xlabel "Servers";' || 'plot ''-'' with lines;' ;
:plot_query;
\set QUIET yes
\t\a\f
\unset QUIET
\o
barwick@localhost:~$ psql -U postgres testdb
psql (9.2.3)
Type "help" for help.
testdb=# \set plot_query 'SELECT * FROM plot'
testdb=# \i tmp/plot.psql
My Graph
4 ++---------+-----------+----------+----------+-----------+---------**
+ + + + + + **** +
| **** |
3.5 ++ **** ++
| **** |
| **** |
3 ++ **** ++
| **** |
2.5 ++ ***** ++
| **** |
| **** |
2 ++ **** ++
| **** |
| **** |
1.5 ++ **** ++
| **** |
+ **** + + + + + +
1 **---------+-----------+----------+----------+-----------+---------++
1 1.5 2 2.5 3 3.5 4
Servers
testdb=#
Ian Barwick
