mysql中TIMESTAMP类型和其他的类型有点不一样(在没有设置explicit_defaults_for_timestamp=1的情况下）
1、在默认情况下，如果TIMESTAMP列没有显式的指明null属性，那么该列会被自动加上not null属性(而其他类型的列如果没有被显式的指定not null，那么是允许null值的)，如果往这个列中插入null值，会自动的设置该列的值为current timestamp值
2、表中的第一个TIMESTAMP列，如果没有指定null属性或者没有指定默认值，也没有指定ON UPDATE语句。那么该列会自动被加上DEFAULT CURRENT_TIMESTAMP和ON UPDATE CURRENT_TIMESTAMP属性。
3、第一个TIMESTAMP列之后的其他的TIMESTAMP类型的列，如果没有指定null属性，也没有指定默认值，那么该列会被自动加上DEFAULT '0000-00-00 00:00:00'属性。如果insert语句中没有为该列指定值，那么该列中插入'0000-00-00 00:00:00'，并且没有warning
如果我们在启动的时候在配置文件中指定了explicit_defaults_for_timestamp=1，mysql会按照如下的方式处理TIMESTAMP 列
1、此时如果TIMESTAMP列没有显式的指定not null属性，那么默认的该列可以为null，此时向该列中插入null值时，会直接记录null，而不是current timestamp。
2、不会自动的为表中的第一个TIMESTAMP列加上DEFAULT CURRENT_TIMESTAMP 和ON UPDATE CURRENT_TIMESTAMP属性，除非你在建表的时候显式的指明
3、如果TIMESTAMP列被加上了not null属性，并且没有指定默认值。这时如果向表中插入记录，但是没有给该TIMESTAMP列指定值的时候，如果strict sql_mode被指定了，那么会直接报错。如果strict sql_mode没有被指定，那么会向该列中插入'0000-00-00 00:00:00'并且产生一个warning
文章最后更新时间：
2019年01月17日 21:26:51
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