How to store the result of multiple select queries into one csv file?
far as i know not possible if you want append one table after another to same file. But you can get them to same file using union 

SQL:

select f.id as fid , null sid   from first f union select null fid , s.id sid from second s


that would create file where all data from first table are
1;null
2;null
....
and second table 
null;1
null;2 

or you can use psql command line tool in linux and call :

psql mydb -c "select id,name from first; " &gt;&gt; myOutFile.txt
psql mydb -c "select id,salary,father_name from second; " &gt;&gt; myOutFile.txt
psql mydb -c "select id,score,bonus,extra from third; " &gt;&gt; myOutFile.txt


In *nix, the > (greater than) character operator redirects output to a file, overwriting the file. 

When doubled, the >> operator redirects output to a file appending the redirected output at the end.