CREATE TABLE table_20715 ("Institution" TEXT, "Location" TEXT, "Team Nickname" TEXT, "Joined TSCHL" FLOAT, "Home Arena" TEXT, "Capacity" FLOAT, "Team Website" TEXT)

What year did the university of Pittsburgh school join the hockey league?
SELECT "Joined TSCHL" FROM table_20715 WHERE "Institution" = 'University of Pittsburgh'
SELECT "Joined TSCHL" FROM "table_20715" WHERE "Institution" = 'University of Pittsburgh'