I've a problem with a trigger in PostgreSQL.
I can do the query but I don't know to develop a trigger.
The example query is:

    select schemaA.table1.value
    from schemaB.table2
    on
    st_contains(schemaB.table2.geom,schemaA.table1.geom)

where geomA is a point geometry and geomB is a polygon geometry.

How can I do this?