更新值而不是NULL

Question

我正在使用Oracle SQL.

我有下表:

Timestamp             | A   | B
13-11-14 06.49.54.004 | 50  | 70
13-11-14 06.49.54.005 | NULL| 80
13-11-14 06.49.54.006 | NULL| NULL
13-11-14 06.49.54.007 | 40  | 70
13-11-14 06.49.54.008 | 20  | 90
13-11-14 06.49.54.009 | 30  | NULL

如何将NULL值替换为每列的最后一个值？这是预期的输出表:

Timestamp             | A   | B
13-11-14 06.49.54.004 | 50  | 70
13-11-14 06.49.54.005 | 50  | 80
13-11-14 06.49.54.006 | 50  | 80
13-11-14 06.49.54.007 | 40  | 70
13-11-14 06.49.54.008 | 20  | 90
13-11-14 06.49.54.009 | 30  | 90

请指教.

Answer 1

您可以将first_value()分析函数与windowing子句一起使用,使用timestamp列进行排序并忽略空值:

select timestamp, a, b,
  first_value(a) ignore nulls over (order by timestamp desc
    rows between current row and unbounded following) as new_a,
  first_value(b) ignore nulls over (order by timestamp desc
    rows between current row and unbounded following) as new_b
from table_name
order by timestamp;

TIMESTAMP                             A          B      NEW_A      NEW_B
---------------------------- ---------- ---------- ---------- ----------
13-NOV-14 06.49.54.004000000         50         70         50         70 
13-NOV-14 06.49.54.005000000                    80         50         80 
13-NOV-14 06.49.54.006000000                               50         80 
13-NOV-14 06.49.54.007000000         40         70         40         70 
13-NOV-14 06.49.54.008000000         20         90         20         90 
13-NOV-14 06.49.54.009000000         30                    30         90 

或者使用last_value()改为:

select timestamp, a, b,
  last_value(a) ignore nulls over (order by timestamp
    rows between unbounded preceding and current row) as new_a,
  last_value(b) ignore nulls over (order by timestamp
    rows between unbounded preceding and current row) as new_b
from table_name
order by timestamp;

该窗口包含当前行,因此如果该值不为null,则将使用该值; 否则它将使用第一个/最后一个非空值(因为该ignore null子句),因为它以指定的顺序遍历窗口.