How many donors have endowment for school named "Glenn"?
SELECT count(DISTINCT T1.donator_name) FROM endowment AS T1 JOIN school AS T2 ON T1.school_id  =  T2.school_id WHERE T2.school_name  =  "Glenn"
donors = donator_name; endowment refers to a relationship or an attribute in the endowment table; school named 'Glenn' refers to school_name = 'Glenn'; count of donors refers to COUNT(DISTINCT donator_name);