Ben Fractenberg/THE CITY At the end of a news conference in Brooklyn last week, THE CITY asked mayoral candidate Andrew Yang what he thought about using pattern bargaining to deal with municipal unions. “I’ll get back to you on that,” he responded before walking away to take selfies with passersby at Parkside Plaza, outside Prospect Park. The century-long practice of giving each public-sector union essentially the same raises and benefit boosts is at the heart of how the city has negotiated with labor organizations representing some 300,000 workers. With the June 22 Democratic primary less than a month away, several of the major hopefuls have notched endorsements from various municipal unions.