开窗函数over(partition by .. [order by ..])用法

1、/** 创建表 */

create table test_orer_partition_by

(

prov_name varchar(20),

city_name varchar(50),

val_cnt int

) ;

2、/** 插入测试数据 */

insert into test_orer_partition_by values ('GS', 'LZ', 234) ;

insert into test_orer_partition_by values ('GS', 'BY', 34) ;

insert into test_orer_partition_by values ('GS', 'DX', 4) ;

insert into test_orer_partition_by values ('GS', 'LN', 67) ;

insert into test_orer_partition_by values ('GS', 'GN', 67) ;

insert into test_orer_partition_by values ('GS', 'QY', 67) ;

insert into test_orer_partition_by values ('SX', 'XA', 34) ;

insert into test_orer_partition_by values ('SX', 'YA', 85) ;

insert into test_orer_partition_by values ('SX', 'BJ', 254) ;

insert into test_orer_partition_by values ('SX', 'HZ', 99) ;

insert into test_orer_partition_by values ('SX', 'XY', 100) ;

insert into test_orer_partition_by values ('SX', 'SL', 23) ;

3、排序（row_number、rank、dense_rank）

3.1 /** row_number() over(partition by prov_name ORDER BY val_cnt) */

select prov_name, city_name, val_cnt,

row_number() over(partition by prov_name ORDER BY val_cnt) AS rst

from test_orer_partition_by ;

3.2 /** rank() over(partition by prov_name ORDER BY val_cnt) */

select prov_name, city_name, val_cnt,

rank() over(partition by prov_name) AS rst

from test_orer_partition_by ;

3.3 /** dense_rank() over(partition by prov_name ORDER BY val_cnt) */

select prov_name, city_name, val_cnt,

dense_rank() over(partition by prov_name ORDER BY val_cnt) AS rst

from test_orer_partition_by ;

4、聚合函数（sum、avg、count、max、min、first_value、last_value）

/** sum() over([partition by prov_name [ORDER BY val_cnt]]) */

有order by；按照排序连续累加；无order by，计算partition by后的和；over()中没有partition by，计算所有数据总和

select prov_name, city_name, val_cnt,

sum(val_cnt) over(partition by prov_name ORDER BY val_cnt) AS rst

from test_orer_partition_by ;

select prov_name, city_name, val_cnt,

sum(val_cnt) over(partition by prov_name) AS rst

from test_orer_partition_by ;

select prov_name, city_name, val_cnt,

sum(val_cnt) over() AS rst

from test_orer_partition_by ;

vg、count、max、min、first_value、last_value与sum用法一模一样，不在赘述。

5、分许函数（lag、lead）

/** lead() over([partition by prov_name [ORDER BY val_cnt]]) */

lag、lead有三个参数，第一个是表达式或字段，第二个是偏移量，第三个是为控制赋值

select prov_name, city_name, val_cnt,

lead(val_cnt, 1) over(partition BY prov_name ORDER BY val_cnt) AS rst

from test_orer_partition_by ;

select prov_name, city_name, val_cnt,

lead(val_cnt, 2) over(partition BY prov_name ORDER BY val_cnt) AS rst

from test_orer_partition_by ;

lag与lead用法相同，只是偏移顺序相反。