SQL to concatenate column values from multiple rows

There are a few ways depending on what version you have

http://www.oracle-base.com/articles/misc/StringAggregationTechniques.php

SELECT pid, LISTAGG(Desc, ' ') WITHIN GROUP (ORDER BY seq) AS desc
FROM   B
GROUP BY pid;

Then join to A to pick out the pids you want.

http://stackoverflow.com/questions/4686543/sql-to-concatenate-column-values-from-multiple-rows