Question

How to make query like this in Java and get the results:

SELECT filedata.num,st_area(ST_Difference(ST_TRANSFORM(filedata.the_geom,70066),filedata_temp.the_geom))
FROM filedata, filedata_temp
Where filedata.num=filedata_temp.num

Or, I think will be better if I create procedure in Postgres from this query.

CREATE OR REPLACE FUNCTION get_geom_difference()
RETURNS void AS
$$
BEGIN
SELECT filedata.num,st_area(ST_Difference(ST_TRANSFORM(filedata.the_geom,70066),filedata_temp.the_geom))
FROM filedata, filedata_temp
Where filedata.num=filedata_temp.num

end;
$$
LANGUAGE 'plpgsql'

and call it

Connection ce_proc= null;
ce_proc = DriverManager.getConnection("jdbc:postgresql://localhost:5432/postgis","postgres","123456");
java.sql.CallableStatement proc =  ce_proc.prepareCall("{get_geom_difference()}");
proc.execute();
proc.close();
ce_proc.close();

But how to get results from this procedure in Java?

UPDATE

I tried this SP

DROP FUNCTION get_geom_difference();

CREATE OR REPLACE FUNCTION get_geom_difference()
RETURNS integer AS
$$
DECLARE

tt integer;
BEGIN
SELECT filedata.num INTO tt
FROM filedata
Where filedata.num=1;
RETURN tt;

END;
$$
LANGUAGE 'plpgsql'

and call

Class.forName("org.postgresql.Driver");
Connection connect= null;
connect = DriverManager.getConnection("jdbc:postgresql://localhost:5432/postgis","postgres","123456");
java.sql.CallableStatement proc =  connect.prepareCall("{?=call get_geom_difference()}");
proc.registerOutParameter(1, java.sql.Types.INTEGER);
proc.executeQuery(); 
ResultSet results = (ResultSet) proc.getObject(1);

and got an error:

org.apache.jasper.JasperException: An exception occurred processing
JSP page /commit_changes.jsp at line 25in lineproc.executeQuery();

root cause javax.servlet.ServletException:
org.postgresql.util.PSQLException: No results were returned by the
query

But query

SELECT filedata.num 
FROM filedata
Where filedata.num=1;

returns 1.

Where is mistake?

Answer 1

You can largely simplify the function. (Keeping simplistic function for the sake of the question.)

CREATE OR REPLACE FUNCTION get_geom_difference()
   RETURNS integer AS
$BODY$
   SELECT num
   FROM   filedata
   WHERE  num = 1 
   LIMIT  1;  -- needed if there can be more than one rows with num = 1
$BODY$    LANGUAGE SQL;

Though, technically, what you have in the question would work, too – provided the data type matches. Does it? Is the column filedata.num of type integer? That’s what I gather from the example. On your other question I was assumingnumeric for lack of information. At least one of them will fail.

If the return type of the function doesn’t match the returned value you get an error from the PostgreSQL function. Properly configured, your PostgreSQL log would have detailed error messages in this case.

What do you see, when you create the above function in PostgreSQL and then call:

SELECT get_geom_difference(1);

from psql. (Preferably in the same session to rule out a mixup of databases, ports, servers or users.)

Calling a simple function taking one parameter and returning one scalar value seems pretty straight forward. Chapter 6.1 of the PostgreSQL JDBC manual has a full example which seems to agree perfectly with what you have in your question (My expertise is with Postgres rather than JDBC, though).