如何获取每个 id 的特定行？

Question

要了解具有多种状态的业务流程，

我想根据created_at 列获取具有以下规则的行：

• 第一行状态‘created’

• ‘missing_info’ 之后的最后一行 ‘created’ (row_no 4)

• ‘pending’ 的第一行（row_no 5）

• ‘missing_info’ 之后的最后一行 ‘pending’ (row_no 7)

• ‘pending’ 在'missing_info' 之后的第一行（row_no 8）

• ‘successful’ 的最后一行（row_no 10）

下面我突出显示了我要检索的行。

这是DB-FIDDLE上的示例数据

以下是一般流程：已创建 > missing_info > 待处理 > 成功。但也只能是这样：创建 > 成功。

我知道我可以将QUALIFY 与窗口函数一起使用，并且可以得到'created' 和'successful'，如下所示。但我不知道如何获得临时状态。我怎样才能达到预期的输出？

created AS(

SELECT *

FROM t1

WHERE status = 'created'

QUALIFY ROW_NUMBER() OVER (PARTITION BY STATUS, id ORDER BY created_at) = 1 )

请注意created 和successful 是开始和结束状态，所以输出中只有一行。其他像 missing_info 或 pending 是临时状态，因此可以在所需的输出中包含多个。

---

编辑：

要了解具有多种状态的业务流程，

我想根据created_at 列获取一些具有以下两条规则的行：

• “待定”之前状态“missing_info”的最后一行（第 2 行）

• 待定（第 3 行）

• “待定”之前状态“missing_info”的最后一行（第 5 行）

• 待定（第 6 行）

示例数据：

WITH t1 AS (

SELECT 'A' AS id, 'missing_info' AS status, '2021-07-15 11:10:00'::timestamp AS created_at UNION ALL

SELECT 'A' AS id, 'missing_info' AS status, '2021-07-15 11:20:00'::timestamp AS created_at UNION ALL

SELECT 'A' AS id, 'pending' AS status, '2021-07-15 11:30:00'::timestamp AS created_at UNION ALL

SELECT 'A' AS id, 'missing_info' AS status, '2021-07-15 12:10:00'::timestamp AS created_at UNION ALL

SELECT 'A' AS id, 'missing_info' AS status, '2021-07-15 12:20:00'::timestamp AS created_at UNION ALL

SELECT 'A' AS id, 'pending' AS status, '2021-07-15 12:30:00'::timestamp AS created_at

    )

SELECT *

FROM t1

期望的输出：

Answer 1

Snowflake 实现了 MATCH_RECOGNIZE，这是在纯 SQL 中查找复杂模式的最简单工具：

识别一组行中的模式匹配。 MATCH_RECOGNIZE 接受一组行（来自表、视图、子查询或其他源）作为输入，并返回该组内给定行模式的所有匹配项。该模式的定义类似于正则表达式。

数据准备：

CREATE OR REPLACE TABLE t
AS
WITH t1 AS (
SELECT 'A' AS id, 'created' AS status, '2021-07-15 10:30:00'::timestamp AS created_at UNION ALL
SELECT 'A' AS id, 'created' AS status, '2021-07-15 10:38:00'::timestamp AS created_at UNION ALL
SELECT 'A' AS id, 'missing_info' AS status, '2021-07-15 11:10:00'::timestamp AS created_at UNION ALL
SELECT 'A' AS id, 'missing_info' AS status, '2021-07-15 11:12:00'::timestamp AS created_at UNION ALL
SELECT 'A' AS id, 'pending' AS status, '2021-07-15 12:05:00'::timestamp AS created_at UNION ALL
SELECT 'A' AS id, 'missing_info' AS status, '2021-07-15 13:36:00'::timestamp AS created_at UNION ALL
SELECT 'A' AS id, 'missing_info' AS status, '2021-07-15 14:36:00'::timestamp AS created_at UNION ALL
SELECT 'A' AS id, 'pending' AS status, '2021-07-15 12:05:00'::timestamp AS created_at UNION ALL
SELECT 'A' AS id, 'successful' AS status, '2021-07-15 16:05:00'::timestamp AS created_at UNION ALL
SELECT 'A' AS id, 'successful' AS status, '2021-07-15 17:00:00'::timestamp AS created_at UNION ALL
SELECT 'B' AS id, 'created' AS status, '2021-07-16 10:30:00'::timestamp AS created_at UNION ALL
SELECT 'B' AS id, 'created' AS status, '2021-07-16 11:30:00'::timestamp AS created_at UNION ALL
SELECT 'B' AS id, 'successful' AS status, '2021-07-16 12:30:00'::timestamp AS created_at
    )     
SELECT * FROM t1;

查询场景 1：

SELECT *
FROM t
MATCH_RECOGNIZE (
  PARTITION BY ID
  ORDER BY CREATED_AT
  -- MEASURES MATCH_NUMBER() AS m, --LAST/FIRST/CLASSIFIER/...
  ALL ROWS PER MATCH
  PATTERN (c+m+)
  DEFINE
     c AS status='created'
    ,m AS status='missing_info'
    ,p AS status='pending'
    ,s AS status='succesful'
) mr
ORDER BY ID, CREATED_AT;
-- returns rows 1-4

这里的重点是作为 Perl 风格的正则表达式提供的模式。在这里，我们正在寻找由一个或多个“missing_info”完成的一个或多个“create”的模式。

ALL ROWS PER MATCH - 返回所有行，但必要时可以更改为第一行

MEASURES: Specifying Additional Output Columns 可用于提供其他信息，例如 MATCH_NUMBER/MATCH_SEQUENCE_NUMBER/CLASSIFIER 等，具体取决于具体需求。

使用“|”可以在单个查询中提供更多模式（备选）：(c+m+|pm+|...)

---

编辑：

“感谢您的回答！它返回前 4 行。我基本上需要第 1 行和第 4 行。”

一旦确定了组，就可以过滤第一行和最后一行，例如使用QUALIFY。关键是使用我之前提到的MEASURES：

SELECT *
    FROM t
    MATCH_RECOGNIZE (
      PARTITION BY ID
      ORDER BY CREATED_AT
      MEASURES MATCH_NUMBER() AS mn,
               MATCH_SEQUENCE_NUMBER AS msn
      ALL ROWS PER MATCH
      PATTERN (c+m+)
      DEFINE
         c AS status='created'
        ,m AS status='missing_info'
        ,p AS status='pending'
        ,s AS status='succesful'
    ) mr
    QUALIFY (ROW_NUMBER() OVER(PARTITION BY mn, ID ORDER BY msn) = 1)
          OR(ROW_NUMBER() OVER(PARTITION BY mn, ID ORDER BY msn DESC)=1)
    ORDER BY ID, CREATED_AT;
    -- returns first and last row by group consisted of ID and MATCH_NUMBER