Actualice varias filas con claves conocidas sin insertar nuevas filas si se encuentran claves inexistentes

Puede intentar generar una tabla de literales y actualizar elementos uniéndose a la tabla:

UPDATE items
    JOIN (SELECT 1 as item_id, 50 as views
          UNION ALL
          SELECT 2 as item_id, 60 as views
          UNION ALL
          SELECT 3 as item_id, 70 as views
          UNION ALL
          SELECT 5 as item_id, 10 as views
          ) as updates
         USING(item_id)
 SET items.views = updates.views;