Question

我有这个表，我必须用最后一个非空值填充值。空值可以是连续的（一个或多个）。

|    date    | value |
+------------+-------+
| 2021-01-05 | NULL  |
| 2021-01-04 | NULL  |
| 2021-01-03 | 3     |
| 2021-01-02 | NULL  |
| 2021-01-01 | 1     |
+------------+-------+

预期结果

|    date    | value |
+------------+-------+
| 2021-01-05 | 3     |
| 2021-01-04 | 3     |
| 2021-01-03 | 3     |
| 2021-01-02 | 1     |
| 2021-01-01 | 1     |
+------------+-------+

我已经尝试过这个，但它不适用于两个连续的空值。如何设置从最后一个非空到当前行的范围？如果第一个值为NULL（例如2020-12-31 IS null）怎么办？

SELECT

    date, 
    last_VALUE(val) 
        OVER(
            PARTITION BY scope_field
            ORDER BY date desc
            RANGE BETWEEN '1 day' PRECEDING AND '1 day' FOLLOWING
        ) last_val
FROM table

Answer 1

使用array_agg()窗函数：

SELECT date,
       COALESCE(value, values[array_upper(values, 1)]::int) AS value
FROM (
  SELECT *,
         array_agg(value::varchar) FILTER (WHERE value IS NOT NULL) OVER (ORDER BY date) AS values
  FROM tablename    
) t  
ORDER BY date DESC

参见demo。

使用 Last_value() 用 Last not null 填充空值

1 个答案: