sql/presto：如何查找每一天之前存在但不是当天的记录

Question

我有如下数据：

 item day
  a   1
  b   1 
  c   1
  a   2
  c   2
  d   2
  a   3 
  d   3

并且期望的结果是为每一天找到在这一天之前消失的记录。期望的结果：

disappeared_item   day_of_interest
        b           2   (as of the second day, only b disappeared)
       b,c          3   (as of the fourth day, b and c disappeared)

我想找出每个项目的最大（天）数，但在如何获得每天累积的项目方面得到了堆栈

Answer 1

WITH 
items AS ( SELECT DISTINCT item
           FROM test ),
days AS ( SELECT DISTINCT day
           FROM test )
SELECT GROUP_CONCAT(items.item) disappeared_item,
       days.day day_of_interest
FROM items
CROSS JOIN days
WHERE EXISTS ( SELECT NULL 
               FROM test
               WHERE test.item = items.item
                 AND test.day < days.day )
  AND NOT EXISTS ( SELECT NULL 
                   FROM test
                   WHERE test.item = items.item
                     AND test.day = days.day )
GROUP BY days.day;

https://dbfiddle.uk/?rdbms=mysql_8.0&fiddle=c35dbe8b9b0a0e00f69c542a70be4bfc