如果我删除MySQL列而不先删除其索引会发生什么？ [英] What happens if I drop a MySQL column without dropping its index first?

问题描述

使用我的一个MySQL表，我删除了列 col1 ，然后从包含它的唯一索引（col0，col1，col2，col3）中删除它。

With one of my MySQL tables, I dropped column col1 before I drop it from a unique index (col0, col1, col2, col3) that contains it.

MySQL会自动处理吗？在删除列col1之后，以前（col0，col1，col2，col3）的唯一索引似乎自动更改为（col0，col2，col3）。

Is it automatically taken care of by MySQL? It seems the unique index that was previously (col0, col1, col2, col3) was automatically changed to (col0, col2, col3) after I deleted the column col1.

它是一个问题还是我必须删除唯一索引并将其重新创建为（col0，col2，col3）？

Is it going to be a problem or do I have to drop the unique index and re-create it as (col0, col2, col3)?

推荐答案

根据 MySQL 5.1参考手册：

如果从表中删除列，
列也会从任何
索引中删除他们是一部分。如果构成索引的所有
列都是
，那么索引也会被删除。
如果您使用CHANGE或MODIFY来缩短
a列，其中
列上的索引存在，并且结果列
长度小于索引长度
MySQL会自动缩短索引
。

If columns are dropped from a table, the columns are also removed from any index of which they are a part. If all columns that make up an index are dropped, the index is dropped as well. If you use CHANGE or MODIFY to shorten a column for which an index exists on the column, and the resulting column length is less than the index length, MySQL shortens the index automatically.

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