Answer by taking a quote from the following article:

Graziano was the son of Ida Scinto and Nicola Barbella. Barbella, nicknamed Fighting Nick Bob, was a boxer with a brief fighting record. Born in Brooklyn, Graziano later moved to an Italian enclave centered on East 10th Street, between First Avenue and Avenue A in Manhattan's East Village. He grew up as a street fighter and learned to look after himself before he could read or write.

As he grew older and seeing no other way to raise his standard of living, Graziano signed a few boxing contracts, but the rigors of training disinterested him. He and his early managers went their separate ways but eventually, he was picked up by Irving Cohen who had the sense to give him a long leash. Cohen changed the young fighter's name from Barbella to Graziano (his grandfather's surname) and lined up a fight. Refusing to train much, Graziano nevertheless showed his killer instinct and won by a knockout. Other fights were lined up with Cohen trying, in his subtle way, to overmatch Graziano, get him defeated, and thereby show him the value of getting into condition. He even demanded a match against Sugar Ray Robinson.  In March 1945, at Madison Square Garden, Graziano scored a major upset over Billy Arnold, whose style was similar to that of Sugar Ray Robinson; he was a slick boxer with lightning-fast combinations and a knockout punch. The Ring magazine and various newspapers across the United States touted Arnold as the next Joe Louis or Sugar Ray Robinson. Arnold was a heavy favorite to defeat Graziano and then to go on to fight for the world title, but Graziano absorbed a beating in the early going, before going on to batter and knock Arnold out in the third round of the scheduled eight-round bout. Following his defeat to Graziano, Arnold was never the same.  Graziano is most famous for his three title bouts with Tony Zale, all for the middleweight title. In their first match (September 27, 1946), after flooring Graziano in the first round, Zale took a savage beating from him, and was on the verge of losing the fight by TKO. However, he rallied and knocked him out in the sixth round to retain his title. The rematch, a year later in Chicago (July 16, 1947), was a mirror image of their first fight. The referee almost stopped the second fight in the third round because of a severe cut over Graziano's left eye, which would have awarded the victory to Zale, but Graziano's cutman, Morris ("Whitey") Bimstein, was able to stop the bleeding to let the fight continue. Graziano was battered around the ring, suffered a closed eye and appeared ready to lose by a knockout, then rallied and knocked Zale out in the sixth round, becoming world middleweight champion. Their last fight was held in New Jersey the following year (June 10, 1948). Zale regained his crown, winning the match by a knockout in the third round. The knockout blows consisted of a perfect combination of a right to Graziano's body, then a left hook to his jaw. He was knocked unconscious. His last attempt at the middleweight title came in April 1952, when he fought Sugar Ray Robinson. He dropped him to his knee with a right in the third round. Less than a minute later, Robinson knocked him out for the count with a right to the jaw. He retired after losing his very next fight, a 10-round decision to Chuck Davey.

How many championships did he win?