POSTGIS Query

[Sven Schroeter]

Hallo,
in a mapserver-project I want to start a query for 2 postggis-layers:

select a.id, b.nom from table_a as a, table_b as b where within (a.the_geom, 
b.the_geom)=true and nom='test';

now I want to delete all datasets from table_a I get as result. How can I 
set a delete statement in one sql-query with this selection?

Thank you
Sven