ssard-完全同意。应该是可能的。我从js udf开始，因为它更简单、更直截了当：o）我会在两次旅行之间尝试纯sql-我这周在加勒比海，海上的连通性不好：o）@ElliottBrossard-我想我明白了。见第二个答案：好！“我仍在试图推出一个只使用SQ

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ssard-完全同意。应该是可能的。我从js udf开始，因为它更简单、更直截了当：o）我会在两次旅行之间尝试纯sql-我这周在加勒比海，海上的连通性不好：o）@ElliottBrossard-我想我明白了。见第二个答案：好！“我仍在试图推出一个只使用SQL的版本……我觉得这一定是可能的。”ElliottBrossard-完全同意。应该是可能的。我从js udf开始，因为它更简单、更直截了当：o）我会在两次旅行之间尝试纯sql-我这周在加勒比海，海上的连通性不好：o）@ElliottBrossard-我想我明白了。请参见第二个答案：o）：D看到基于SQL的解决方案非常酷。不是说JavaScript不好玩，而是感觉像作弊哈哈。很好，谢谢！我想知道使用

unest

和

array\u agg

的子查询/cte比使用

string\u agg

和

split

更好。有什么想法吗？纯SQL被认为是最好的，并且没有JSUDF相关的限制：看到基于SQL的解决方案非常酷。不是说JavaScript不好玩，而是感觉像作弊哈哈。很好，谢谢！我想知道使用

unest

和

array\u agg

的子查询/cte比使用

string\u agg

和

split

更好。有什么想法吗？纯SQL被认为是最好的，并且没有JSUDF相关的限制

datetime | event  | value
==========================
1        | add    | 1
---------+--------+-------
2        | remove | 1
---------+--------+-------
6        | add    | 2
---------+--------+-------
8        | add    | 3
---------+--------+-------
11       | add    | 4
---------+--------+-------
23       | remove | 3
---------+--------+-------

datetime | event  | value | list
===================================
1        | add    | 1     | [1]
---------+--------+-------+--------
2        | remove | 1     | []
---------+--------+-------+--------
6        | add    | 2     | [2]
---------+--------+-------+--------
8        | add    | 3     | [2,3]
---------+--------+-------+--------
11       | add    | 4     | [2,3,4]
---------+--------+-------+--------
23       | remove | 3     | [2,4]
---------+--------+-------+--------

#standardSQL
CREATE TEMP FUNCTION CUST_ARRAY_AGG(arr ARRAY<STRUCT<event STRING, value STRING>>)
RETURNS ARRAY<STRING>
LANGUAGE js AS """
  var result = [];  
  for (i = 0; i < arr.length; i++) { 
    if (arr[i].event == 'add') {
      result.push(arr[i].value);
    } else {
      var index = result.indexOf(arr[i].value);
      if (index > -1) {
        result.splice(index, 1);
      }
    }
  }
  return result;
""";
WITH `project.dataset.events` AS (
  SELECT 1 dt, 'add' event, '1' value UNION ALL
  SELECT 2, 'remove', '1' UNION ALL
  SELECT 6, 'add', '2' UNION ALL
  SELECT 8, 'add', '3' UNION ALL
  SELECT 11, 'add', '4' UNION ALL
  SELECT 23, 'remove', '3' 
)
SELECT dt, event, value, 
  CUST_ARRAY_AGG(arr) list_as_arr,
  (SELECT CONCAT('[', IFNULL(STRING_AGG(item), ''), ']') FROM UNNEST(CUST_ARRAY_AGG(arr)) item) list_as_string
FROM (
  SELECT dt, event, value,
    ARRAY_AGG(STRUCT<event STRING, value STRING>(event, value)) OVER(ORDER BY dt) arr
  FROM `project.dataset.events`
)

Row dt  event   value   list_as_arr list_as_string   
1   1   add     1       1           [1]  
2   2   remove  1                   []   
3   6   add     2       2           [2]  
4   8   add     3       2           [2,3]    
                        3        
5   11  add     4       2           [2,3,4]  
                        3        
                        4        
6   23  remove  3       2           [2,4]    
                        4   

#standardSQL
WITH `project.dataset.events` AS (
  SELECT 1 dt,'add' event,'1' value UNION ALL
  SELECT 2,   'remove',   '1' UNION ALL
  SELECT 6,   'add',      '2' UNION ALL
  SELECT 8,   'add',      '3' UNION ALL
  SELECT 11,  'add',      '4' UNION ALL
  SELECT 23,  'remove',   '3' 
), cum AS (
  SELECT dt, event, value,
    SUM(IF(event = 'add', 1, -1)) OVER(PARTITION BY value ORDER BY dt) state
  FROM `project.dataset.events`
), pre AS (
  SELECT 
    a.dt, a.event, a.value, a.state, b.value AS b_value,
    ARRAY_AGG(b.state ORDER BY b.dt DESC)[SAFE_OFFSET(0)] b_state, 
    MAX(b.dt) b_dt 
  FROM cum a
  JOIN cum b ON b.dt <= a.dt
  GROUP BY a.dt, a.event, a.value, a.state, b.value
)
SELECT dt, event, value, 
  SPLIT(IFNULL(STRING_AGG(IF(b_state = 1, b_value, NULL) ORDER BY b_dt), '')) list_as_array,
  CONCAT('[', IFNULL(STRING_AGG(IF(b_state = 1, b_value, NULL) ORDER BY b_dt), ''), ']') list_as_string
FROM pre
GROUP BY dt, event, value
ORDER BY dt  

Row dt  event   value   list_as_arr list_as_string   
1   1   add     1       1           [1]  
2   2   remove  1                   []   
3   6   add     2       2           [2]  
4   8   add     3       2           [2,3]    
                        3        
5   11  add     4       2           [2,3,4]  
                        3        
                        4        
6   23  remove  3       2           [2,4]    
                        4   

#standardSQL
-- stolen test table ;)
WITH test AS (
  SELECT 1 dt,'add' event,'1' value UNION ALL
  SELECT 2,   'remove',   '1' UNION ALL
  SELECT 6,   'add',      '2' UNION ALL
  SELECT 8,   'add',      '3' UNION ALL
  SELECT 11,  'add',      '4' UNION ALL
  SELECT 23,  'remove',   '3' 
)

, windowing as (
SELECT *,
  -- add history using window function
  ARRAY_AGG(STRUCT(event, value)) OVER ( ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) as history
FROM test)

SELECT 
  dt,
  event,
  value,
  --history, -- for testing

  -- Get all added items that are not removed items
  -- This sub-select runs within the row only, treating history-array as (sub-)table
  (SELECT ARRAY_AGG(value) value FROM unnest(t.history) l 
    WHERE l.event = 'add' 
    AND l.value NOT IN 
      (SELECT l.value FROM unnest(t.history) l WHERE l.event = 'remove')
  ) AS list
FROM windowing t

DECLARE arr ARRAY<STRUCT<dt INT64, event STRING, value STRING>>;
DECLARE result ARRAY<STRUCT<dt INT64, event STRING, value STRING, list STRING>> DEFAULT [STRUCT(NULL, '', '', '')];
DECLARE list ARRAY<STRING> DEFAULT [];
DECLARE i, m INT64 DEFAULT -1; 

SET arr = (
  WITH t AS (
    SELECT 1 dt,'add' event,'1' value UNION ALL
    SELECT 2,   'remove',   '1' UNION ALL
    SELECT 6,   'add',      '2' UNION ALL
    SELECT 8,   'add',      '3' UNION ALL
    SELECT 11,  'add',      '4' UNION ALL
    SELECT 23,  'remove',   '3' 
  )
  SELECT ARRAY_AGG(t) FROM t
);

SET m = ARRAY_LENGTH(arr);

LOOP
  SET i = i + 1;
  IF i >= m THEN LEAVE;
  ELSE
    IF arr[OFFSET(i)].event = 'add' THEN 
      SET list = (
        SELECT ARRAY_CONCAT(list, [arr[OFFSET(i)].value])
      );    
    ELSE
      SET list = ARRAY(
        SELECT item
        FROM UNNEST(list) item 
        WHERE item != arr[OFFSET(i)].value
      );    
    END IF;

    SET result = (
      SELECT ARRAY_CONCAT(
        result, 
        [(arr[OFFSET(i)].dt, arr[OFFSET(i)].event, arr[OFFSET(i)].value, ARRAY_TO_STRING(list, ','))]
      )
    );
  END IF;
END LOOP;

SELECT * FROM UNNEST(result) WHERE NOT dt IS NULL;