Postgresql - ROW_NUM(), RANK() 和 DENSE_RANK() 的区别

pigdb=# WITH T(CateID, ID)
     AS (SELECT 1,1 UNION ALL
         SELECT 1,1 UNION ALL
         SELECT 1,1 UNION ALL
         SELECT 1,2)
SELECT *,
       RANK() OVER(PARTITION BY CateID ORDER BY ID) ,
       ROW_NUMBER() OVER(PARTITION BY CateID ORDER BY ID),
       DENSE_RANK() OVER(PARTITION BY CateID ORDER BY ID)
FROM   T;
 cateid | id | rank | row_number | dense_rank
--------+----+------+------------+------------
      1 |  1 |    1 |          1 |          1
      1 |  1 |    1 |          2 |          1
      1 |  1 |    1 |          3 |          1
      1 |  2 |    4 |          4 |          2
(4 rows)