Hello,
I have a program that executes SQL statements and returns XML to the client where it is converted to a dataset and used afterwards. Written in Object Pascal this is working with no problems over TCP/IP.
Now I have written that in Perl to work over HTTP and have some problems. With Pascal's classes it is very easy to obtain the data type and column size after a SELECT query is executed. For this to work I am using $dbh->column_info() as wriiten in DBI docs.
The problem is that this one needs a column name and a table name.
A simple sql parser is doing fine but when it comes to JOIN queries this gets dirty.
A simple query like:
can be written in numerous ways and there is much more work to be done to determine correct column type and size.

Is there an easy way to use column_info with JOIN queries, or any other way for getting this information? I have searched the net and column_info seems to be very used function. Not to mention easy migration in DB systems.

Thanks in advance!

Your question ranges from vague to incomprehensible.

You seem to think that joins make a query result really complicated. They don't. The result of a query with a join subclause is just a regular SQL table. So getting info on the columns is going to work the same way it does without joins.

If you're asking, "can I ask the DBMS what the schema looks like before I build a dynamic query," the answer is "depends on the DBMS you're using." DBI is, like ODBC, JDBC, ADO and on and on, pretty much a wrapper around SQL. Operations like interrogating the schema of the database are usually handled by proprietary SQL. You might search your DBMS manual for INFORMATION_SCHEMA.

If you're trying to figure out what the "schema" of your result is, then, again, it depends on your DBMS but there are a slew of functions in DBI. Read The Fine Manual on DBI, meaning "man DBI" or go to http://dbi.perl.org/.