Se demora demasiado mi consulta

[younothing_14]

Alguien me puede ayudar con este query, demora mucho al procesar, gracias

select matri.id_dtmatricula, cur.id_dtcurso, t.id_dtiempo,

(select count(*) as can_alu_aprob from tmatdetalles where (matpromediofinal>=11 and matpromediofinal<=20))can_alu_aprob,
(select count(*) as can_alu_desap from tmatdetalles where (matpromediofinal>=1 and matpromediofinal<=10))can_alu_desap,
(select count(*) as can_alu_c_obser from tmatdetalles where (notaobs is not null))can_alu_c_obser

from tmatdetalles det, dtmatricula matri, dtcurso cur, talumnos alu, dtiempo t
where det.matcodigo=matri.matcodigo and matri.alucodigo=alu.alucodigo and det.curcodigo=cur.curcodigo and det.fechaeval is not null