how many teams have used the stadium which hosted the swimming at the 1908 summer olympics – men's 100 metre freestyle ?
SELECT DISTINCT COUNT attr_open var_uri attr_close where brack_open dbr_Swimming_at_the_1908_Summer_Olympics_–_Men's_100_metre_freestyle dbp_venue var_x sep_dot var_x dbo_tenant var_uri sep_dot var_x a dbo_Stadium brack_close