南大通用GBase 8a OLAP分析函数NTILE的使用样例

GBase 8a的NTILE函数，将数据切分成指定的几块，如果且不均匀，则前面的优先。本文介绍NTILE的用法和使用样例。

语法

NTILE(num) OVER([PARTITION BY col_name1,col_name2,…] ORDER BY col_name1 [asc/desc], col_name2 [asc/desc],…)

说明

num参数是指定切成几块。 第一块值为1，第二块为2，以此类推。

如果一个窗口内的数据，无法均匀的分成指定块数，则优先填充前面的。

样例

数据

gbase> create table td(id int, type int,val decimal(20,3));
Query OK, 0 rows affected (Elapsed: 00:00:00.17)

gbase> insert into td values(1,1,111),(1,1,222),(2,1,333),(2,2,444),(3,2,555),(3,2,666),(4,2,777);
Query OK, 7 rows affected (Elapsed: 00:00:00.12)
Records: 7  Duplicates: 0  Warnings: 0

gbase> insert into td values(5,1,null),(50,2,null);
Query OK, 2 rows affected (Elapsed: 00:00:00.09)
Records: 2  Duplicates: 0  Warnings: 0

gbase> select * from td;
+------+------+---------+
gbase> select * from td order by type;
+------+------+---------+
| id   | type | val     |
+------+------+---------+
|    1 |    1 | 222.000 |
|    2 |    1 | 333.000 |
|    5 |    1 |    NULL |
|    1 |    1 | 111.000 |
|    3 |    2 | 666.000 |
|    4 |    2 | 777.000 |
|    3 |    2 | 555.000 |
|    2 |    2 | 444.000 |
|   50 |    2 |    NULL |
+------+------+---------+
9 rows in set (Elapsed: 00:00:00.04)

标准NTILE用法

type=2里有5个，分不均匀，分块1为3个，分块2为2个。

gbase> select *,ntile(2)over(partition by type order by id) maxOfType from td;
+------+------+---------+-----------+
| id   | type | val     | maxOfType |
+------+------+---------+-----------+
|    1 |    1 | 111.000 |         1 |
|    1 |    1 | 222.000 |         1 |
|    2 |    1 | 333.000 |         2 |
|    2 |    2 | 444.000 |         1 |
|    3 |    2 | 555.000 |         1 |
|    3 |    2 | 666.000 |         1 |
|    4 |    2 | 777.000 |         2 |
|    5 |    1 |    NULL |         2 |
|   50 |    2 |    NULL |         2 |
+------+------+---------+-----------+
9 rows in set (Elapsed: 00:00:00.35)

无partition的NTILE

所有数据分成2块。

gbase> select *,ntile(2)over(order by id) maxOfType from td;
+------+------+---------+-----------+
| id   | type | val     | maxOfType |
+------+------+---------+-----------+
|    1 |    1 | 111.000 |         1 |
|    1 |    1 | 222.000 |         1 |
|    2 |    1 | 333.000 |         1 |
|    2 |    2 | 444.000 |         1 |
|    3 |    2 | 555.000 |         1 |
|    3 |    2 | 666.000 |         2 |
|    4 |    2 | 777.000 |         2 |
|    5 |    1 |    NULL |         2 |
|   50 |    2 |    NULL |         2 |
+------+------+---------+-----------+
9 rows in set (Elapsed: 00:00:00.08)

无order的NTILE

自然顺序，不保证每次相同。

gbase> select *,ntile(2)over(partition by type) maxOfType from td;
+------+------+---------+-----------+
| id   | type | val     | maxOfType |
+------+------+---------+-----------+
|    1 |    1 | 111.000 |         2 |
|    1 |    1 | 222.000 |         1 |
|    2 |    1 | 333.000 |         1 |
|    2 |    2 | 444.000 |         2 |
|    3 |    2 | 555.000 |         1 |
|    3 |    2 | 666.000 |         1 |
|    4 |    2 | 777.000 |         1 |
|    5 |    1 |    NULL |         2 |
|   50 |    2 |    NULL |         2 |
+------+------+---------+-----------+
9 rows in set (Elapsed: 00:00:00.07)

无Partition和order的NTILE

gbase> select *,ntile(2)over() maxOfType from td;
+------+------+---------+-----------+
| id   | type | val     | maxOfType |
+------+------+---------+-----------+
|    1 |    1 | 111.000 |         1 |
|    1 |    1 | 222.000 |         1 |
|    2 |    1 | 333.000 |         1 |
|    2 |    2 | 444.000 |         1 |
|    3 |    2 | 555.000 |         1 |
|    3 |    2 | 666.000 |         2 |
|    4 |    2 | 777.000 |         2 |
|    5 |    1 |    NULL |         2 |
|   50 |    2 |    NULL |         2 |
+------+------+---------+-----------+
9 rows in set (Elapsed: 00:00:00.29)