Bunu kullanın..

$count = mysql_num_rows(mysql_query("select baslik,aciklama,id,parent,ara from haberler where baslik LIKE '%$search%' or aciklama LIKE '%$search%' union
select adi,aciklama,id,parent,ara from birimler where adi LIKE '%$search%' or aciklama LIKE '%$search%' union
select baslik,aciklama,id,parent,ara from mevzuat where baslik LIKE '%$search%' or aciklama LIKE '%$search%' union
select baslik,icerik,id,parent,ara from duyurular where baslik LIKE '%$search%' or icerik LIKE '%$search%' union
select baslik,aciklama,id,parent,ara from yonetim where baslik LIKE '%$search%' or aciklama LIKE '%$search%'"));