Question

I have a somewhat detailed query in a script that uses ? placeholders. I wanted to test this same query directly from the psql command line (outside the script). I want to avoid going in and replacing all the ? with actual values, instead I’d like to pass the arguments after the query.

Example:

SELECT  * 
FROM    foobar
WHERE   foo = ?
   AND  bar = ?
    OR  baz = ?  ;

Looking for something like:

%> {select * from foobar where foo=? and bar=? or baz=? , 'foo','bar','baz' };

Answer 1

You can use the -v option e.g:

$ psql -v v1=12 -v v2="'Hello World'" -v v3="'2010-11-12'"

and then refer to the variables in SQL as :v1, :v2 etc:

select * from table_1 where id = :v1;

Please pay attention to how we pass string/date values using two quotes " '...' " But this way of interpolation is prone to SQL injections, because it’s you who’s responsible for quoting. E.g. need to include a single quote? -v v2="'don''t do this'".

A better/safer way is to let PostgreSQL handle it:

$ psql -c 'create table t (a int, b varchar, c date)'
$ echo "insert into t (a, b, c) values (:'v1', :'v2', :'v3')" \
  | psql -v v1=1 -v v2="don't do this" -v v3=2022-01-01