用连接中的最后一个可用值替换零值

Question

我正在使用 SQL 服务器。

编辑：之前使用了一个错误 SQL Fiddle - 已更新以更正一个

连接语句：

select t1.A_NR, t1.V_DATE, t1.AMOUNT T1_AMOUNT, t2.AMOUNT T2_AMOUNT
from Table_1 t1 
left join Table_2 t2 on t1.A_NR = t2.A_NR and t1.V_DATE = t2.V_DATE

给我带来了这个 table，在 T2_Amount 行中有空值。

+------+----------------------+-----------+-----------+
| A_NR |        V_DATE        | T1_AMOUNT | T2_AMOUNT |
+------+----------------------+-----------+-----------+
|    1 | 2020-01-01T00:00:00Z |       100 | 100       |
|    1 | 2020-01-02T00:00:00Z |       101 | (null)    |
|    1 | 2020-01-03T00:00:00Z |       102 | (null)    |
|    2 | 2020-01-01T00:00:00Z |       200 | 200       |
|    2 | 2020-01-02T00:00:00Z |       201 | (null)    |
|    2 | 2020-01-03T00:00:00Z |       202 | (null)    |
+------+----------------------+-----------+-----------+

我想用 Table_2 中的最后可用值替换这些值，如下所示：

+------+----------------------+-----------+-----------+
| A_NR |        V_DATE        | T1_AMOUNT | T2_AMOUNT |
+------+----------------------+-----------+-----------+
|    1 | 2020-01-01T00:00:00Z |       100 |       100 |
|    1 | 2020-01-02T00:00:00Z |       101 |       100 | -->  value from 01.01.2020
|    1 | 2020-01-03T00:00:00Z |       102 |       100 | -->  value from 01.01.2020
|    2 | 2020-01-01T00:00:00Z |       200 |       200 |
|    2 | 2020-01-02T00:00:00Z |       201 |       200 | -->  value from 01.01.2020
|    2 | 2020-01-03T00:00:00Z |       202 |       200 | -->  value from 01.01.2020
+------+----------------------+-----------+-----------+

Answer 1

一个选项使用相关子查询或横向连接：

select t1.a_nr, t1.v_date, t1.amount as t1_amount, t2.* 
from table_1 t1 
outer apply (
    select top (1) t2.amount as t2_amount
    from table_2 t2 
    where t2.a_nr = t1.a_nr and t2.v_date <= t1.v_date
    order by t2.v_date desc
) t2

另一种方法是使用一些间隙和孤岛技术：我们可以将不匹配的记录与具有 window 计数的最新匹配记录一起分组，然后使用 window 最大值来恢复我们想要的值：

select a_nr, v_date, amount as t1_amount, 
    max(t2_amount) over(partition by a_nr, grp)
from (
    select t1.*, t2.amount as t2_amount,
        count(t2.amount) over(partition by t1.a_nr order by t1.v_date) as grp
    from table_1 t1 
    left join table_2 t2 on t2.a_nr = t1.a_nr and t2.v_date = t1.v_date
) t

用连接中的最后一个可用值替换零值

Replace zero values with last available value in join

sql

sql-server

datetime

left-join

gaps-and-islands