mysql的datetime与timestamp设置null对比

版本:5.7

结论：对于NOT NULL DEFAULT current_timestamp()，若是timestamp类型设置为null会被设置成当前时间，而对于datetime会报错

1.timestamp类型

CREATE TABLE `table_1` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(100) DEFAULT NULL,
  `create_time` timestamp(6) NOT NULL DEFAULT current_timestamp(6) COMMENT '创建时间',
   PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin ;

insert into table_1(name, create_time) values('1', null);

select * from table_1;

结果：

 2.datetime类型

CREATE TABLE `table_2` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(100) DEFAULT NULL,
  `create_time` datetime NOT NULL DEFAULT current_timestamp() COMMENT '创建时间',
   PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin ;


insert into table_2(name, create_time) values('1', null)

结果：

参考文档

MySQL :: MySQL 5.7 Reference Manual :: 11.2.6 Automatic Initialization and Updating for TIMESTAMP and DATETIMEhttps://dev.mysql.com/doc/refman/5.7/en/timestamp-initialization.html

 In addition, if the explicit_defaults_for_timestamp system variable is disabled, you can initialize or update any TIMESTAMP (but not DATETIME) column to the current date and time by assigning it a NULL value, unless it has been defined with the NULL attribute to permit NULL values.