Ask about Inner Join & Union
Try This

SELECT A.*,B.mat_nama,C.mats_nama 
FROM pengeluaran AS A 
INNER JOIN material AS B ON A.mat_id = B.mat_id 
INNER JOIN mat_satuan AS C ON B.mat_satuan_id = C.mats_id
WHERE A.mat_id = '7'
   AND A.pengeluaran_tgl BETWEEN '2014-01-01'  AND '2014-02-28'

UNION

SELECT A.*,B.mat_nama,C.mats_nama
FROM penerimaan_sub AS A 
INNER JOIN material AS B ON A.mat_id = B.mat_id
INNER JOIN mat_satuan AS C ON B.mat_satuan_id = C.mats_id
WHERE A.mat_id = '7'
  AND A.penerimaan_tgl BETWEEN '2014-01-01' AND '2014-01-28'