从创建日期开始按年龄范围分组的 SQL 查询

Question

我想通过 sql 查询获取统计信息。我的表是这样的：

ID MATERIAL CREATEDATE DEPARTMENT
1  M1       10.10.1980 D1
2  M2       11.02.1970 D2
2  M3       18.04.1971 D3
.....................
.....................
.....................

我怎样才能获得这样的数据计数范围

DEPARTMENT AGE<10  10<AGE<20 20<AGE
D1         24       123      324
D2         24       123      324

Answer 1

假设 CREATEDATE 是一个日期列，在 PostgreSQL 中你可以使用AGE函数：

select DEPARTMENT, age(CREATEDATE) as AGE
from Materials

使用 date_part 您可以获得以年为单位的年龄。要以您想要的格式显示数据，您可以使用这个 GROUP BY 查询：

select
  DEPARTMENT,
  sum(case when date_part('year', age(CREATEDATE))<10 then 1 end) as "age<10",
  sum(case when date_part('year', age(CREATEDATE))>=10 and date_part('year', age(CREATEDATE))<20 then 1 end) as "10<age<20",
  sum(case when date_part('year', age(CREATEDATE))>=20 then 1 end) as "20<age"
from
  Materials
group by
  DEPARTMENT

可以简化为：

with mat_age as (
  select DEPARTMENT, date_part('year', age(CREATEDATE)) as mage
  from Materials
)
select
  DEPARTMENT,
  sum(case when mage<10 then 1 end) as "age<10",
  sum(case when mage>=10 and mage<20 then 1 end) as "10<age<20",
  sum(case when mage>=20 then 1 end) as "20<age"
from
  mat_age
group by
  DEPARTMENT;

如果您使用的是 PostgreSQL 9.4，则可以使用 FILTER：

with mat_age as (
  select DEPARTMENT, date_part('year', age(CREATEDATE)) as mage
  from Materials
)
select
  DEPARTMENT,
  count(*) filter (where mage<10) as "age<10",
  count(*) filter (where mage>=10 and mage<20) as "10<age<20",
  count(*) filter (where mage>=20) as "20<age"
from
  mat_age
group by
  DEPARTMENT;