Postgres 递归 CTE 或交叉表函数

Question

我尝试从包含日志信息的表中生成一些用户统计信息。

**TABLE users**
user_id | user_name
-------------------
1       | julia
2       | bob
3       | sebastian


**TABLE logs**
user_id | action        | timepoint
------------------------------------
1       | create_quote  | 2015-01-01
1       | send_quote    | 2015-02-03
1       | create_quote  | 2015-02-02
1       | start_job     | 2015-01-15
2       | start_job     | 2015-02-23
2       | send_quote    | 2015-03-04
2       | start_job     | 2014-12-02

我想要的输出如下表

user_id | username  | create_quote | send_quote | start_job
-----------------------------------------------------------
1       | julia     |2             | 1          | 1
2       | bob       |0             | 1          | 1
3       | sebastian |0             | 0          | 0

它包括所有用户（即使没有记录任何内容），但仅包括日期“2015-01-01”和“2015-05-31”之间的操作。操作按操作类型和用户进行计数/分组。

SQL 语句可能看起来像

SELECT * FROM myfunction() WHERE to_char(timepoint, 'YY/MM') BETWEEN '15/01' AND '15/05';

您知道如何管理吗？我一直在尝试 CTE 和递归以及交叉表函数，但找不到任何解决方案。

Answer 1

我认为交叉表功能会更优雅，但如果您没有加载扩展程序，或者像我一样在语法上遇到困难，这是一种笨拙的蛮力方式可以做到：

CREATE OR REPLACE FUNCTION get_stats(
    from_date date,
    thru_date date)
  RETURNS table (
    user_id integer, 
    username text, 
    create_quote bigint, 
    send_quote bigint,
    start_job bigint
  )  AS
$BODY$
  select
    l.user_id, u.username,
    sum (case when action = 'create_quote' then 1 else 0 end) as create_quote,
    sum (case when action = 'send_quote' then 1 else 0 end) as send_quote,
    sum (case when action = 'start_job' then 1 else 0 end) as start_job
  from
    logs l
    join users u on l.user_id = u.user_id
  where
    l.timepoint between from_date and thru_date
  group by
    l.user_id, u.username
$BODY$
  LANGUAGE sql VOLATILE
  COST 100
  ROWS 1000;

然后您的查询将是：

select * from get_stats('2015-01-01', '2015-05-31')

就个人而言，我会跳过该函数并将其创建为查询，但可以想象，您需要函数包装器是有原因的。

-- 编辑--

根据尝试的编辑，我知道您可能会接受查询。此外，您希望用户没有条目。

考虑到所有这些，我认为这可能可行：

  select
    u.user_id, u.username,
    sum (case when action = 'create_quote' then 1 else 0 end) as create_quote,
    sum (case when action = 'send_quote' then 1 else 0 end) as send_quote,
    sum (case when action = 'start_job' then 1 else 0 end) as start_job
  from
    users u
    left join logs l on
       l.user_id = u.user_id and
       l.timepoint between '2015-01-01' and '2015-05-31'
  group by
    u.user_id, u.username