In businesses with a category of "DJs", how many businesses are rated less than 5?
category of "DJs" refers to category_name = 'DJs'; rated less than 5 refers to stars < 5; businesses refer to business_id;
SELECT COUNT(T1.business_id) FROM Business AS T1 INNER JOIN Business_Categories AS T2 ON T1.business_id = T2.business_id INNER JOIN Categories AS T3 ON T2.category_id = T3.category_id WHERE T3.category_name = 'DJs' AND T1.stars < 5