如何在MySQL中将零值替换为先前的非零值？

Question

免责声明：这不是重复的问题。发布之前我已经研究了

红色圆圈中的值应为“ 2”，因为先前的非零值是数字2。如何在mysql更新查询中做到这一点？如您所见，还有其他具有相同零值的行需要具有先前的非零值。

Answer 1

您可以使用内联查询：

select 
    pk,
    case when val1 = 0 
        then (select val1 from mytable t1 where t1.pk < t.pk and t1.val1 != 0 order by pk desc limit 1)
        else val1
    end val1,
    val2,
    val3,
    received_date
from mytable t

Answer 2

如果只想选择正确的值，请使用

  select pk, val1, @previous as previous_v, @previous := val1
  from your_table
  cross join (select @previous := 0) p
  order by pk

如果您还想更新表，请使用

update your_table t
join
(
  select pk, val1, @previous as previous_v, @previous := val1
  from your_table
  cross join (select @previous := 0) p
  order by pk
) tmp on tmp.pk = t.pk
set t.val1 = previous_v
where t.val1 = 0

SQLFiddle demo