窗口函数
窗口函数
列存表目前只支持rank(expression)和row_number(expression)两个函数。
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。窗口函数用于给组内的值生成序号。
示例：
--创建表。
openGauss=# CREATE TABLE t2 (c1 INT, c2 INT);
--导入数据。
openGauss=# INSERT INTO t2 SELECT generate_series, generate_series FROM generate_series(1, 1000000);
--执行查询，查询正常无报错，且执行结果正确。
openGauss=# EXPLAIN ANALYZE SELECT nc1 FROM (
SELECT row_number() over() rid,
t2.c1 nc1
FROM t2
) WHERE rid BETWEEN 1 AND (1 + 10 - 1);
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------
Subquery Scan on __unnamed_subquery__ (cost=0.00..0.42 rows=3 width=4) (actual time=0.201..0.228 rows=10 loops=1)
Filter: (__unnamed_subquery__.rid >= 1)
-> WindowAgg (cost=0.00..0.30 rows=10 width=4) (actual time=0.191..0.211 rows=10 loops=1)
row_number_filter: (row_number() OVER () <= 10)
-> Seq Scan on t2 (cost=0.00..11977.45 rows=817445 width=4) (actual time=0.150..0.153 rows=11 loops=1)
Total runtime: 0.539 ms
(6 rows)
--环境清理，避免数据泄露。
openGauss=# DROP TABLE t2;
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：
openGauss=# 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：
openGauss=# 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：
openGauss=# 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：
openGauss=# 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：
openGauss=# 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：
openGauss=# 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：
openGauss=# 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：
openGauss=# 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：
openGauss=# 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：
openGauss=# 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：
openGauss=# 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：
td_db=# insert into test_any_value values(1,1),(2,1),(3,2),(4,2); INSERT 0 4 td_db=# select row_count(); row_count ----------- 4 (1 row)
意见反馈