v5.0

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)

row_count()

描述：上一条语句影响的行数。
- 若上次执行的是DDL语句，比如create table或者drop语句，会返回0。
对于insert/update/delete语句，以及其他会涉及元组修改的语句，会返回具体影响的行数。
- 对于select语句，若为select into, 会返回导出的元组数量，反之若语句不涉及修改则返回-1。
返回值类型：BIGINT

示例：
```
MogDB=# insert into test_any_value values(1,1),(2,1),(3,2),(4,2);
INSERT 0 4
MogDB=# select row_count();
row_count
-----------
        4
(1 row)
```

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