如何修改 MySQL 列以允许 NULL?

How do I modify a MySQL column to allow NULL?(如何修改 MySQL 列以允许 NULL?)

问题描述

MySQL 5.0.45

MySQL 5.0.45

更改表以允许列为空的语法是什么，或者这有什么问题:

What is the syntax to alter a table to allow a column to be null, alternately what's wrong with this:

ALTER mytable MODIFY mycolumn varchar(255) null;

我将手册解释为只是运行上面的内容，它会重新创建列，这次允许为空.服务器告诉我我有语法错误.我只是没有看到他们.

I interpreted the manual as just run the above and it would recreate the column, this time allowing null. The server is telling me I have syntactical errors. I just don't see them.

推荐答案

您需要以下内容:

ALTER TABLE mytable MODIFY mycolumn VARCHAR(255);

列默认可以为空.只要该列未声明为 UNIQUE 或 NOT NULL，就不会有任何问题.

Columns are nullable by default. As long as the column is not declared UNIQUE or NOT NULL, there shouldn't be any problems.

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