[英](SQL) How to conditionally filter based on a value calculated using OVER
I have a log of customers going through a workflow. 我有通过工作流程的客户日志。 I want to do two things, and I am struggling with either of them. 我想做两件事,而我都在努力。
First is: I wish to filter out customers who didn't start by entering the first state at the beginning of the workflow (enter state 0). 首先是:我希望通过在工作流开始时输入第一个状态(输入状态0)来筛选出没有开始的客户。
Second is: For remaining customers I want to know how much time they spent in each step of the workflow. 其次是:对于剩余的客户,我想知道他们在工作流程的每个步骤中花费了多少时间。
Each record has: 每条记录都有:
I tried to do a query that would allow me to get the timestamp of entry and exit grouped by customer and state like so: 我尝试执行一个查询,该查询将允许我获取按客户和状态分组的进入和退出的时间戳,如下所示:
SELECT
CUSTOMER_ID,
STATE,
MIN(UPDATE_DT) AS ENTRY_DATE,
MAX(UPDATE_DT) AS EXIT_DATE
FROM LOG_DATA
GROUP BY CUSTOMER_ID, STATE
ORDER BY CUSTOMER_ID, STATE;
But I immediately run into a few problems. 但是我立即遇到了一些问题。 The query will run just fine but: 该查询将正常运行,但:
I tried to focus on the first problem by introducing an additional attribute in my select thusly: 我试图通过在选择中引入一个附加属性来关注第一个问题:
MIN(STATE) OVER(PARTITION BY CUSTOMER_ID) AS EARLIEST_STATE
But then ran into a few problems. 但是随后遇到了一些问题。 I am unable to include EARLIEST_STATE as a condition of the WHERE or the GROUP BY HAVING because to the WHERE it does not exist, and the GROUP BY will not allow me to include EARLIEST_STATE. 我无法将EARLIEST_STATE包含为WHERE或GROUP BY HAVING的条件,因为对于WHERE而言,它不存在,并且GROUP BY不允许我包含EARLIEST_STATE。
As I thought this through it gets worse - MIN(STATE) can only prove, at best, customer has STATE = 0 but not that they have a record that says ACTION = "enter" and STATE = 0. So this approach fails not only because I can't get it to run but because it's also logically not correct. 正如我所认为的那样,这种情况变得越来越糟-MIN(STATE)最多只能证明客户的STATE = 0,但不能证明他们有一条记录说ACTION =“ enter”和STATE =0。所以这种方法不仅失败因为我无法让它运行,但因为从逻辑上讲也是不正确的。
I know I could do multiple SELECT with SELECTs but this feels clunky and I want to learn the right way to do this. 我知道我可以对SELECT进行多个SELECT,但这感觉很笨拙,我想学习正确的方法。 It also doesn't help that I am dealing with 10 million rows of data so efficiency is important. 处理1000万行数据也无济于事,因此效率很重要。
I am using Postgres 9.5, I have no control over either the DB technology or the schema of the data in this instance. 我使用的是Postgres 9.5,在这种情况下我无法控制数据库技术或数据模式。
It would be slow but I could use something my Python to do this, but I would really like to know the correct way to do this using the DB. 这会很慢,但是我可以使用我的Python来执行此操作,但是我真的很想知道使用数据库执行此操作的正确方法。
If I understand correctly, you want at least one row with Action = 'Enter'
and state = 0
for any customer that is in the result set. 如果我理解正确,那么对于结果集中的任何客户,您都希望至少有一行行,其中Action = 'Enter'
并且state = 0
。 That suggests a window function: 这暗示了一个窗口函数:
SELECT CUSTOMER_ID, STATE,
MIN(UPDATE_DT) AS ENTRY_DATE,
MAX(UPDATE_DT) AS EXIT_DATE,
FROM (SELECT l.*,
SUM(CASE WHEN ACTION = 'Enter' AND state = 0 THEN 1 ELSE 0 END) OVER (PARTITION BY CUSTOMER_ID) as num_validenter
FROM LOG_DATA l
) l
WHERE num_validenter > 0
GROUP BY CUSTOMER_ID, STATE
ORDER BY CUSTOMER_ID, STATE
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