窗口函数（分析函数）

窗口函数与OVER语句一起使用。OVER语句用于对数据进行分组，并对组内元素进行排序。

说明: 窗口函数中的order by后面必须跟字段名，若order by后面跟数字，该数字会被按照常量处理，因此对目标列没有起到排序的作用。

• RANK()

  描述：RANK函数为各组内值生成跳跃排序序号，其中，相同的值具有相同序号。

  返回值类型：BIGINT

  示例：

  MogDB=# SELECT d_moy, d_fy_week_seq, rank() OVER(PARTITION BY d_moy ORDER BY d_fy_week_seq) FROM tpcds.date_dim WHERE d_moy < 4 AND d_fy_week_seq < 7 ORDER BY 1,2;
     d_moy | d_fy_week_seq | rank
  -------+---------------+------
       1 |             1 |    1
       1 |             1 |    1
       1 |             1 |    1
       1 |             1 |    1
       1 |             1 |    1
       1 |             1 |    1
       1 |             1 |    1
       1 |             2 |    8
       1 |             2 |    8
       1 |             2 |    8
       1 |             2 |    8
       1 |             2 |    8
       1 |             2 |    8
       1 |             2 |    8
       1 |             3 |   15
       1 |             3 |   15
       1 |             3 |   15
       1 |             3 |   15
       1 |             3 |   15
       1 |             3 |   15
       1 |             3 |   15
       1 |             4 |   22
       1 |             4 |   22
       1 |             4 |   22
       1 |             4 |   22
       1 |             4 |   22
       1 |             4 |   22
       1 |             4 |   22
       1 |             5 |   29
       1 |             5 |   29
       2 |             5 |    1
       2 |             5 |    1
       2 |             5 |    1
       2 |             5 |    1
       2 |             5 |    1
       2 |             6 |    6
       2 |             6 |    6
       2 |             6 |    6
       2 |             6 |    6
       2 |             6 |    6
       2 |             6 |    6
       2 |             6 |    6
  (42 rows)

• ROW_NUMBER()

  描述：ROW_NUMBER函数为各组内值生成连续排序序号，其中，相同的值其序号也不相同。

  返回值类型：BIGINT

  示例：

  MogDB=# SELECT d_moy, d_fy_week_seq, Row_number() OVER(PARTITION BY d_moy ORDER BY d_fy_week_seq) FROM tpcds.date_dim  WHERE d_moy < 4 AND d_fy_week_seq < 7 ORDER BY 1,2;
   d_moy | d_fy_week_seq | row_number
  -------+---------------+------------
       1 |             1 |          1
       1 |             1 |          2
       1 |             1 |          3
       1 |             1 |          4
       1 |             1 |          5
       1 |             1 |          6
       1 |             1 |          7
       1 |             2 |          8
       1 |             2 |          9
       1 |             2 |         10
       1 |             2 |         11
       1 |             2 |         12
       1 |             2 |         13
       1 |             2 |         14
       1 |             3 |         15
       1 |             3 |         16
       1 |             3 |         17
       1 |             3 |         18
       1 |             3 |         19
       1 |             3 |         20
       1 |             3 |         21
       1 |             4 |         22
       1 |             4 |         23
       1 |             4 |         24
       1 |             4 |         25
       1 |             4 |         26
       1 |             4 |         27
       1 |             4 |         28
       1 |             5 |         29
       1 |             5 |         30
       2 |             5 |          1
       2 |             5 |          2
       2 |             5 |          3
       2 |             5 |          4
       2 |             5 |          5
       2 |             6 |          6
       2 |             6 |          7
       2 |             6 |          8
       2 |             6 |          9
       2 |             6 |         10
       2 |             6 |         11
       2 |             6 |         12
  (42 rows)

• DENSE_RANK()

  描述：DENSE_RANK函数为各组内值生成连续排序序号，其中，相同的值具有相同序号。

  返回值类型：BIGINT

  示例：

  MogDB=# SELECT d_moy, d_fy_week_seq, dense_rank() OVER(PARTITION BY d_moy ORDER BY d_fy_week_seq) FROM tpcds.date_dim WHERE d_moy < 4 AND d_fy_week_seq < 7 ORDER BY 1,2;
   d_moy | d_fy_week_seq | dense_rank
  -------+---------------+------------
       1 |             1 |          1
       1 |             1 |          1
       1 |             1 |          1
       1 |             1 |          1
       1 |             1 |          1
       1 |             1 |          1
       1 |             1 |          1
       1 |             2 |          2
       1 |             2 |          2
       1 |             2 |          2
       1 |             2 |          2
       1 |             2 |          2
       1 |             2 |          2
       1 |             2 |          2
       1 |             3 |          3
       1 |             3 |          3
       1 |             3 |          3
       1 |             3 |          3
       1 |             3 |          3
       1 |             3 |          3
       1 |             3 |          3
       1 |             4 |          4
       1 |             4 |          4
       1 |             4 |          4
       1 |             4 |          4
       1 |             4 |          4
       1 |             4 |          4
       1 |             4 |          4
       1 |             5 |          5
       1 |             5 |          5
       2 |             5 |          1
       2 |             5 |          1
       2 |             5 |          1
       2 |             5 |          1
       2 |             5 |          1
       2 |             6 |          2
       2 |             6 |          2
       2 |             6 |          2
       2 |             6 |          2
       2 |             6 |          2
       2 |             6 |          2
       2 |             6 |          2
  (42 rows)

• PERCENT_RANK()

  描述：PERCENT_RANK函数为各组内对应值生成相对序号，即根据公式 (rank - 1) / (total rows - 1)计算所得的值。其中rank为该值依据RANK函数所生成的对应序号，totalrows为该分组内的总元素个数。

  返回值类型：DOUBLE PRECISION

  示例：

  MogDB=# SELECT d_moy, d_fy_week_seq, percent_rank() OVER(PARTITION BY d_moy ORDER BY d_fy_week_seq) FROM tpcds.date_dim WHERE d_moy < 4 AND d_fy_week_seq < 7 ORDER BY 1,2;
   d_moy | d_fy_week_seq |   percent_rank
  -------+---------------+------------------
       1 |             1 |                0
       1 |             1 |                0
       1 |             1 |                0
       1 |             1 |                0
       1 |             1 |                0
       1 |             1 |                0
       1 |             1 |                0
       1 |             2 | .241379310344828
       1 |             2 | .241379310344828
       1 |             2 | .241379310344828
       1 |             2 | .241379310344828
       1 |             2 | .241379310344828
       1 |             2 | .241379310344828
       1 |             2 | .241379310344828
       1 |             3 | .482758620689655
       1 |             3 | .482758620689655
       1 |             3 | .482758620689655
       1 |             3 | .482758620689655
       1 |             3 | .482758620689655
       1 |             3 | .482758620689655
       1 |             3 | .482758620689655
       1 |             4 | .724137931034483
       1 |             4 | .724137931034483
       1 |             4 | .724137931034483
       1 |             4 | .724137931034483
       1 |             4 | .724137931034483
       1 |             4 | .724137931034483
       1 |             4 | .724137931034483
       1 |             5 |  .96551724137931
       1 |             5 |  .96551724137931
       2 |             5 |                0
       2 |             5 |                0
       2 |             5 |                0
       2 |             5 |                0
       2 |             5 |                0
       2 |             6 | .454545454545455
       2 |             6 | .454545454545455
       2 |             6 | .454545454545455
       2 |             6 | .454545454545455
       2 |             6 | .454545454545455
       2 |             6 | .454545454545455
       2 |             6 | .454545454545455
  (42 rows)

• CUME_DIST()

  描述：CUME_DIST函数为各组内对应值生成累积分布序号。即根据公式(小于等于当前值的数据行数)/(该分组总行数totalrows)计算所得的相对序号。

  返回值类型：DOUBLE PRECISION

  示例：

  MogDB=# SELECT d_moy, d_fy_week_seq, cume_dist() OVER(PARTITION BY d_moy ORDER BY d_fy_week_seq) FROM tpcds.date_dim e_dim WHERE d_moy < 4 AND d_fy_week_seq < 7 ORDER BY 1,2;
   d_moy | d_fy_week_seq |    cume_dist
  -------+---------------+------------------
       1 |             1 | .233333333333333
       1 |             1 | .233333333333333
       1 |             1 | .233333333333333
       1 |             1 | .233333333333333
       1 |             1 | .233333333333333
       1 |             1 | .233333333333333
       1 |             1 | .233333333333333
       1 |             2 | .466666666666667
       1 |             2 | .466666666666667
       1 |             2 | .466666666666667
       1 |             2 | .466666666666667
       1 |             2 | .466666666666667
       1 |             2 | .466666666666667
       1 |             2 | .466666666666667
       1 |             3 |               .7
       1 |             3 |               .7
       1 |             3 |               .7
       1 |             3 |               .7
       1 |             3 |               .7
       1 |             3 |               .7
       1 |             3 |               .7
       1 |             4 | .933333333333333
       1 |             4 | .933333333333333
       1 |             4 | .933333333333333
       1 |             4 | .933333333333333
       1 |             4 | .933333333333333
       1 |             4 | .933333333333333
       1 |             4 | .933333333333333
       1 |             5 |                1
       1 |             5 |                1
       2 |             5 | .416666666666667
       2 |             5 | .416666666666667
       2 |             5 | .416666666666667
       2 |             5 | .416666666666667
       2 |             5 | .416666666666667
       2 |             6 |                1
       2 |             6 |                1
       2 |             6 |                1
       2 |             6 |                1
       2 |             6 |                1
       2 |             6 |                1
       2 |             6 |                1
  (42 rows)

• NTILE(num_buckets integer)

  描述：NTILE函数根据num_buckets integer将有序的数据集合平均分配到num_buckets所指定数量的桶中，并将桶号分配给每一行。分配时应尽量做到平均分配。

  返回值类型：INTEGER

  示例：

  MogDB=# SELECT d_moy, d_fy_week_seq, ntile(3) OVER(PARTITION BY d_moy ORDER BY d_fy_week_seq) FROM tpcds.date_dim WHERE d_moy < 4 AND d_fy_week_seq < 7 ORDER BY 1,2;
   d_moy | d_fy_week_seq | ntile
  -------+---------------+-------
       1 |             1 |     1
       1 |             1 |     1
       1 |             1 |     1
       1 |             1 |     1
       1 |             1 |     1
       1 |             1 |     1
       1 |             1 |     1
       1 |             2 |     1
       1 |             2 |     1
       1 |             2 |     1
       1 |             2 |     2
       1 |             2 |     2
       1 |             2 |     2
       1 |             2 |     2
       1 |             3 |     2
       1 |             3 |     2
       1 |             3 |     2
       1 |             3 |     2
       1 |             3 |     2
       1 |             3 |     2
       1 |             3 |     3
       1 |             4 |     3
       1 |             4 |     3
       1 |             4 |     3
       1 |             4 |     3
       1 |             4 |     3
       1 |             4 |     3
       1 |             4 |     3
       1 |             5 |     3
       1 |             5 |     3
       2 |             5 |     1
       2 |             5 |     1
       2 |             5 |     1
       2 |             5 |     1
       2 |             5 |     2
       2 |             6 |     2
       2 |             6 |     2
       2 |             6 |     2
       2 |             6 |     3
       2 |             6 |     3
       2 |             6 |     3
       2 |             6 |     3
  (42 rows)

• LAG(value any [, offset integer [, default any ]])

  描述：LAG函数为各组内对应值生成滞后值。即当前值对应的行数往前偏移offset位后所得行的value值作为序号。若经过偏移后行数不存在，则对应结果取为default值。若无指定，在默认情况下，offset取为1，default值取为NULL。

  返回值类型：与参数数据类型相同。

  示例：

  MogDB=# SELECT d_moy, d_fy_week_seq, lag(d_moy,3,null) OVER(PARTITION BY d_moy ORDER BY d_fy_week_seq) FROM tpcds.date_dim WHERE d_moy < 4 AND d_fy_week_seq < 7 ORDER BY 1,2;
   d_moy | d_fy_week_seq | lag
  -------+---------------+-----
       1 |             1 |
       1 |             1 |
       1 |             1 |
       1 |             1 |   1
       1 |             1 |   1
       1 |             1 |   1
       1 |             1 |   1
       1 |             2 |   1
       1 |             2 |   1
       1 |             2 |   1
       1 |             2 |   1
       1 |             2 |   1
       1 |             2 |   1
       1 |             2 |   1
       1 |             3 |   1
       1 |             3 |   1
       1 |             3 |   1
       1 |             3 |   1
       1 |             3 |   1
       1 |             3 |   1
       1 |             3 |   1
       1 |             4 |   1
       1 |             4 |   1
       1 |             4 |   1
       1 |             4 |   1
       1 |             4 |   1
       1 |             4 |   1
       1 |             4 |   1
       1 |             5 |   1
       1 |             5 |   1
       2 |             5 |
       2 |             5 |
       2 |             5 |
       2 |             5 |   2
       2 |             5 |   2
       2 |             6 |   2
       2 |             6 |   2
       2 |             6 |   2
       2 |             6 |   2
       2 |             6 |   2
       2 |             6 |   2
       2 |             6 |   2
  (42 rows)

• LEAD(value any [, offset integer [, default any ]])

  描述：LEAD函数为各组内对应值生成提前值。即当前值对应的行数向后偏移offset位后所得行的value值作为序号。若经过向后偏移后行数超过当前组内的总行数，则对应结果取为default值。若无指定，在默认情况下，offset取为1，default值取为NULL。

  返回值类型：与参数数据类型相同。

  示例：

    MogDB=# SELECT d_moy, d_fy_week_seq, lead(d_fy_week_seq,2) OVER(PARTITION BY d_moy ORDER BY d_fy_week_seq) FROM  tpcds.date_dim WHERE d_moy < 4 AND d_fy_week_seq < 7 ORDER BY 1,2;
    d_moy | d_fy_week_seq | lead
    -------+---------------+------
         1 |             1 |    1
         1 |             1 |    1
         1 |             1 |    1
         1 |             1 |    1
         1 |             1 |    1
         1 |             1 |    2
         1 |             1 |    2
         1 |             2 |    2
         1 |             2 |    2
         1 |             2 |    2
         1 |             2 |    2
         1 |             2 |    2
         1 |             2 |    3
         1 |             2 |    3
         1 |             3 |    3
         1 |             3 |    3
         1 |             3 |    3
         1 |             3 |    3
         1 |             3 |    3
         1 |             3 |    4
         1 |             3 |    4
         1 |             4 |    4
         1 |             4 |    4
         1 |             4 |    4
         1 |             4 |    4
         1 |             4 |    4
         1 |             4 |    5
         1 |             4 |    5
         1 |             5 |
         1 |             5 |
         2 |             5 |    5
         2 |             5 |    5
         2 |             5 |    5
         2 |             5 |    6
         2 |             5 |    6
         2 |             6 |    6
         2 |             6 |    6
         2 |             6 |    6
         2 |             6 |    6
         2 |             6 |    6
         2 |             6 |
         2 |             6 |
    (42 rows)

• FIRST_VALUE(value any)

  描述：FIRST_VALUE函数取各组内的第一个值作为返回结果。

  返回值类型：与参数数据类型相同。

  示例：

  MogDB=# SELECT d_moy, d_fy_week_seq, first_value(d_fy_week_seq) OVER(PARTITION BY d_moy ORDER BY d_fy_week_seq) FROM tpcds.date_dim WHERE d_moy < 4 AND d_fy_week_seq < 7 ORDER BY 1,2;
   d_moy | d_fy_week_seq | first_value
  -------+---------------+-------------
       1 |             1 |           1
       1 |             1 |           1
       1 |             1 |           1
       1 |             1 |           1
       1 |             1 |           1
       1 |             1 |           1
       1 |             1 |           1
       1 |             2 |           1
       1 |             2 |           1
       1 |             2 |           1
       1 |             2 |           1
       1 |             2 |           1
       1 |             2 |           1
       1 |             2 |           1
       1 |             3 |           1
       1 |             3 |           1
       1 |             3 |           1
       1 |             3 |           1
       1 |             3 |           1
       1 |             3 |           1
       1 |             3 |           1
       1 |             4 |           1
       1 |             4 |           1
       1 |             4 |           1
       1 |             4 |           1
       1 |             4 |           1
       1 |             4 |           1
       1 |             4 |           1
       1 |             5 |           1
       1 |             5 |           1
       2 |             5 |           5
       2 |             5 |           5
       2 |             5 |           5
       2 |             5 |           5
       2 |             5 |           5
       2 |             6 |           5
       2 |             6 |           5
       2 |             6 |           5
       2 |             6 |           5
       2 |             6 |           5
       2 |             6 |           5
       2 |             6 |           5
  (42 rows)

• LAST_VALUE(value any)

  描述：LAST_VALUE函数取各组内的最后一个值作为返回结果。

  返回值类型：与参数数据类型相同。

  示例：

  MogDB=# SELECT d_moy, d_fy_week_seq, last_value(d_moy) OVER(PARTITION BY d_moy ORDER BY d_fy_week_seq) FROM tpcds.date_dim WHERE d_moy < 4 AND d_fy_week_seq < 6 ORDER BY 1,2;
    d_moy | d_fy_week_seq | last_value
  -------+---------------+------------
       1 |             1 |          1
       1 |             1 |          1
       1 |             1 |          1
       1 |             1 |          1
       1 |             1 |          1
       1 |             1 |          1
       1 |             1 |          1
       1 |             2 |          1
       1 |             2 |          1
       1 |             2 |          1
       1 |             2 |          1
       1 |             2 |          1
       1 |             2 |          1
       1 |             2 |          1
       1 |             2 |          1
       1 |             3 |          1
       1 |             3 |          1
       1 |             3 |          1
       1 |             3 |          1
       1 |             3 |          1
       1 |             3 |          1
       1 |             3 |          1
       1 |             4 |          1
       1 |             4 |          1
       1 |             4 |          1
       1 |             4 |          1
       1 |             4 |          1
       1 |             4 |          1
       1 |             4 |          1
       1 |             5 |          1
       1 |             5 |          1
       2 |             5 |          2
       2 |             5 |          2
       2 |             5 |          2
       2 |             5 |          2
       2 |             5 |          2
  (35 rows)

• NTH_VALUE(value any, nth integer)

  描述：NTH_VALUE函数返回该组内的第nth行作为结果。若该行不存在，则默认返回NULL。

  返回值类型：与参数数据类型相同。

  示例：

  MogDB=# SELECT d_moy, d_fy_week_seq, nth_value(d_fy_week_seq,6) OVER(PARTITION BY d_moy ORDER BY d_fy_week_seq) FROM tpcds.date_dim WHERE d_moy < 4 AND d_fy_week_seq < 6 ORDER BY 1,2;
   d_moy | d_fy_week_seq | nth_value
  -------+---------------+-----------
       1 |             1 |         1
       1 |             1 |         1
       1 |             1 |         1
       1 |             1 |         1
       1 |             1 |         1
       1 |             1 |         1
       1 |             1 |         1
       1 |             2 |         1
       1 |             2 |         1
       1 |             2 |         1
       1 |             2 |         1
       1 |             2 |         1
       1 |             2 |         1
       1 |             2 |         1
       1 |             3 |         1
       1 |             3 |         1
       1 |             3 |         1
       1 |             3 |         1
       1 |             3 |         1
       1 |             3 |         1
       1 |             3 |         1
       1 |             4 |         1
       1 |             4 |         1
       1 |             4 |         1
       1 |             4 |         1
       1 |             4 |         1
       1 |             4 |         1
       1 |             4 |         1
       1 |             5 |         1
       1 |             5 |         1
       2 |             5 |
       2 |             5 |
       2 |             5 |
       2 |             5 |
       2 |             5 |
  (35 rows)

• ratio_to_report

  描述：计算一个值与一组值之和的比率。

  返回类型：float

  示例：

  MogDB=# SELECT last_name, salary, RATIO_TO_REPORT(salary) OVER () AS rr
     FROM employees
     WHERE job_id = 'PU_CLERK'
     ORDER BY last_name, salary, rr;
  -----------------------------------------------
  LAST_NAME                     SALARY         RR
  ------------------------- ---------- ----------
  Baida                           2900 .208633094
  Colmenares                      2500 .179856115
  Himuro                          2600  .18705036
  Khoo                            3100 .223021583
  Tobias                          2800 .201438849