how many teams have used the stadium which hosted the swimming at the 2012 summer olympics – women's 400 metre individual medley ?
SELECT DISTINCT COUNT attr_open var_uri attr_close where brack_open dbr_Swimming_at_the_2012_Summer_Olympics_–_Women's_400_metre_individual_medley dbp_venue var_x sep_dot var_x dbo_tenant var_uri sep_dot var_x a dbo_Stadium brack_close