为了账号安全，请及时绑定邮箱和手机立即绑定

课程

/数据库

/MySQL

/与MySQL的零距离接触

是否允许为空

id SMALLINT,

username VARCHAR(20) NOT NULL

设置username字段不允许为空

但是插入数据的时候，如果只插入id的数据，INSERT user （id） VALUE （' 1 '）；

结果username 的值是个空白，也不提示该值不允许为空。

如果不设置 NOT NULL 则会默认填充 NULL，

难道说设置 NOT NULL  只是为了让默认值=“空白”或者他的值不能为NULL这个值

不设置的话默认值=NULL  就这样的区别？并不能控制该字段必须要填充一个 具体的值进去？

独唱团_0001

2015-11-24

源自：与MySQL的零距离接触  2-10

关注问题 我要回答
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收起

正在回答

4 回答

慕九州0167811
2022-07-20

您好，如果您有什么疑问，可以在这里提问的，我会尽量及时回复您。

scwfmlrdadffgbwnf

0 回复 有任何疑惑可以回复我~
收起回答
qq_慕神1420022
2022-03-31

排序函数，returna-b，返回小于0,a放到数组中比b小的索引号,返回大于0,b放到数组中比a小的索引号。

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0 回复 有任何疑惑可以回复我~
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高恒博
2016-06-20

默认值设置为空了，你show columns from tb1 看下。

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q也会老的曾
2015-11-25

这个应该会报错才对。

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本课程涵盖全部MySQL数据库的基础，学习MySQL数据库的基础知识

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