- From: Richard Cyganiak <richard@cyganiak.de>
- Date: Fri, 21 Oct 2011 14:14:00 +0100
- To: David McNeil <dmcneil@revelytix.com>
- Cc: Fabian Pijcke <fabian.pijcke@gmail.com>, public-rdb2rdf-comments@w3.org
On 21 Oct 2011, at 13:51, David McNeil wrote: > TABLE, PK_COLUMN, PK_COLUMN_ORDER > PERSON, FNAME, 1 > PERSON, LNAME, 2 > > Now you would like to run a query against these tuples to produce an aggregate value (grouped on TABLE) something like "FNAME,LNAME". You need a list of the key columns in a string that you can use in a template in the R2RML mapping. So I see two possibilities: > > 1) write the query you need in SQL - I don't know if this is possible in generic SQL. Not in generic SQL. In MySQL it's easily done with GROUP_CONCAT, and there are equivalents for the other RDBMS but with slightly different syntax. Still, that's the way to go IMO. I don't like the idea of adding features to R2RML with the motivation that SQL isn't portable. R2RML is not a database abstraction layer. Not even string concatenation is portable in SQL – if you do anything non-trivial, you'll have to special-case anyways, that's just a fact of life and we may just as well accept it. Best, Richard
Received on Friday, 21 October 2011 13:14:30 UTC