Window Functions

Currently, column-store tables only support rank(expression) and row_number(expression) functions.

Window functions and the OVER clause are used together. The OVER clause is used for grouping data and sorting the elements in a group. Window functions are used for generating sequence numbers for the values in the group.

NOTE: order by in a window function must be followed by a column name. If it is followed by a number, the number is processed as a constant value and the target column is not ranked.

• RANK()

  Description: Generates non-consecutive sequence numbers for the values in each group. The same values have the same sequence number.

  Return type: bigint

  Example:

  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()

  Description: Generates consecutive sequence numbers for the values in each group. The same values have different sequence numbers.

  Return type: bigint

  Example:

  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()

  Description: Generates consecutive sequence numbers for the values in each group. The same values have the same sequence number.

  Return type: bigint

  Example:

  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()

  Description: Generates corresponding sequence numbers for the values in each group. That is, the function calculates the value according to the formula Sequence number = (rank - 1) / (total rows - 1). rank is the corresponding sequence number generated based on the RANK function for the value and totalrows is the total number of elements in a group.

  Return type: double precision

  Example:

  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()

  Description: Generates accumulative distribution sequence numbers for the values in each group. That is, the function calculates the value according to the following formula: Sequence number = Number of rows preceding or peer with current row/Total rows.

  Return type: double precision

  Example:

  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)

  Description: Equally allocates sequential data sets to the buckets whose quantity is specified by num_buckets according to num_buckets integer and allocates the bucket number to each row. Divide the partition as evenly as possible.

  Return type: integer

  Example:

  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 ]])

  Description: Generates lag values for the corresponding values in each group. That is, the value of the row obtained by moving forward the row corresponding to the current value by offset (integer) is the sequence number. If the row does not exist after the moving, the result value is the default value. If omitted, offset defaults to 1 and default to NULL.

  Return type: same as the parameter type

  Example:

  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 ]])

  Description: Generates leading values for the corresponding values in each group. That is, the value of the row obtained by moving backward the row corresponding to the current value by offset (integer) is the sequence number. If the row after the moving exceeds the total number of rows for the current group, the result value is the default value. If omitted, offset defaults to 1 and default to NULL.

  Return type: same as the parameter type

  Example:

  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)

  Description: Returns the first value of each group.

  Return type: same as the parameter type

  Example:

  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)

  Description: Returns the last value of each group.

  Return type: same as the parameter type

  Example:

  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)

  Description: Returns the _n_th row for a group. If the row does not exist, NULL is returned by default.

  Return type: same as the parameter type

  Example:

  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)