小弟我们在建数据库时，设计表的字段为不为空的作用是什么
我们在建数据库时，设计表的字段为不为空的作用是什么?
像这样，什么时候设计为null，什么时候有必须不为null呢？求解
------解决思路----------------------
不为空的话，就是说那个字段必须有值。
至于什么时候设计为null，什么时候有必须不为null呢？ 这个还得看需求。
------解决思路----------------------
null 空值，表示什么都没有
如果在业务中，某个字段的值是可有可无的，那么就可以设为 null
null 的另一个用途是：可以用于某个数据项是否进行了输入。这在需要多次操作后才能形成完整的记录的场合是非常重要的
------解决思路----------------------
不为空的，在MSSQL里如果改字段没有数据会插入失败，MYSQL里好像是严格模式也会失败。主要是用来约束数据的完整性。
------解决思路----------------------
主要根据业务场景，比如有些字段信息必填，那用户就得必须填写，不然就会提示操作失败。
------解决思路----------------------
好像大数据量搜索的话，字段不为null搜索效率会提高，请大神印证
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