notnull

Though you did not specify that column, the Rails migration created it for you anyway, with auto_increment and NOT NULL.

虽然没有指定这个列，但是Rails迁移会自动创建它，并具有auto_increment和NOTNULL属性。

The following table illustrates the relationship between the existence of a default and the definition of a column as NULL or NOT NULL.

下表说明默认值的存在与将列定义为NULL或NOTNULL之间的关系。

A computed column cannot be used as a DEFAULT or FOREIGN KEY constraint definition or with a NOT NULL constraint definition.

计算列不能用作DEFAULT或FOREIGNKEY约束定义，也不能与NOTNULL约束定义一起使用。

In MySQL, if you try to execute an INSERT statement that does not provide a value for a NOT NULL column, the command is successful.

在MySQL中，如果要执行一个不提供NOTNULL列值的INSERT语句，此命令没有问题。

We recommend that you explicitly specify NULL or NOT NULL for each column in a temporary table.

建议对于临时表中的每列，显式指定NULL或NOTNULL。