I'm trying to create this trigger and getting the following compiler errors:

create or replace
TRIGGER RESTAR_PLAZAS
AFTER INSERT ON PLAN_VUELO
BEGIN
SELECT F.NRO_VUELO, M.CAPACIDAD, M.CAPACIDAD - COALESCE((
SELECT count(*) FROM PLAN_VUELO P
WHERE P.NRO_VUELO = F.NRO_VUELO
       ), 0) as PLAZAS_DISPONIBLES
FROM VUELO F
      INNER JOIN MODELO M ON M.ID = F.CODIGO_AVION; 
END RESTAR_PLAZAS;


Error(2,7): PL/SQL: SQL Statement ignored
Error(8,5): PL/SQL: ORA-00933: SQL command not properly ended
Error(8,27): PLS-00103: Encountered the symbol "end-of-file" when expecting one of the following:     begin case declare end exception exit for goto if loop mod    null pragma raise return select update while with    <an identifier> <a double-quoted delimited-identifier>    <a bind variable> << close current delete fetch lock insert    open rollback savepoint set sql execute commit forall merge    pipe 
Error(2,1): PLS-00428: an INTO clause is expected in this SELECT statement

What's wrong with this trigger?