使用同一表SQL中的日期更新列

Question

我有这个表结构

id | value
---|----------
1  |  0.2
2  |  0.3
3  |  0.5
4  |  0.25
5  |  0.37
6  |  0.56
7  |  
8  |  
9  |  

现在我想用id = 2到5之间的值来更新最后3个元素的值，我这样做是因为听起来很简单

UPDATE table AS z0
SET value = z1.value
FROM table as z1
WHERE z1.id BETWEEN 2 AND 5
AND z0.id BETWEEn 7 AND 9

但是结果是这样的，只是取范围（id = 2）中的第一个元素的值

 id | value
    ---|----------
    1  |  0.2
    2  |  0.3
    3  |  0.5
    4  |  0.25
    5  |  0.37
    6  |  0.56
    7  |  0.3
    8  |  0.3
    9  |  0.3

Answer 1

这样行吗？

update table 
    set value = (select value
                 from table t2
                 where id between 2 and 5
                 order by random()
                 limit 1
                )
    where value is null;

las，上面的方法行不通（尽管我认为应该如此）。 问题在于子查询仅被执行一次。 此版本可以正常工作：

update table t
    set value = (select value
                 from table t2
                 where id between 2 and 5 and t2.id <> t.id
                 order by random()
                 limit 1
                )
    where value is null;

相关子句阻止只运行一次查询的优化。 这是一个SQL Fiddle，它演示了逻辑。

Answer 2

你可以用这个

 UPDATE table AS z0
 SET value = z1.value
 FROM table as z1
 WHERE z1.id = (z0.id - 4)
 AND z0.id BETWEEn 7 AND 9