If I understand your question correctly and you have a parent table and a child table, join the two tables with an INNER JOIN.  This will retrieve only the parent records that have at least one associated child record.

Example:

SELECT * FROM DT_PERSON P INNER JOIN DT_QUALIFICATION Q ON P.Person_ID = Q.Person_ID

If you use a LEFT OUTER JOIN, then parent records without any child records would also be retrieved.

I hope this helps.

Mark