CREATE TABLE table_54391 ("Entrant" TEXT, "Constructor" TEXT, "Chassis" TEXT, "Engine" TEXT, "Tyres" TEXT, "Driver" TEXT, "Rounds" TEXT)

Tell me the constructor for clay regazzoni
SELECT "Constructor" FROM table_54391 WHERE "Driver" = 'clay regazzoni'
SELECT "Constructor" FROM "table_54391" WHERE "Driver" = 'clay regazzoni'