[英]What happens in Oracle when I drop a column?
What are the various things that happen when I drop a column from a filled table. 当我从填充表中删除列时会发生什么样的事情。 In all_tab_columns, does the column_id of other columns get reset?
在all_tab_columns中,其他列的column_id是否会重置?
The actions will include at least the following: 这些行动至少包括以下内容:
alter table drop column alter table drop column
will actually visit each block and remove the column data - and that's an expensive thing to do for a large table. 实际上将访问每个块并删除列数据 - 这对于大型表来说是一件昂贵的事情。
You might find it more prudent to issue: 你可能会发现更谨慎的问题:
alter table set unused alter table set unused
which just flags the column as "gone" in the dictionary. 它只是将列标记为字典中的“已消失”。 If you then still need to reclaim that space, you can schedule an "alter table drop unused" at a quiet time
如果您仍需要回收该空间,则可以在安静的时间安排“未使用alter table drop”
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