how many people have worked for teams chaired by abdullah bin nasser bin abdullah al ahmed al thani ?
SELECT DISTINCT COUNT attr_open var_uri attr_close where brack_open var_x dbo_chairman dbr_Abdullah_bin_Nasser_bin_Abdullah_Al_Ahmed_Al_Thani sep_dot var_x dbp_name var_uri sep_dot var_uri a dbo_Person brack_close