mysql增加和删除字段

• 时间字段：

`create_time` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT \'创建时间\',
`last_update_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT \'最后更新时间\',

• 删除某个字段：

ALTER TABLE `tableName` drop COLUMN `columeName`;

• 增加某个字段：

ALTER TABLE `tableName` ADD COLUMN `columeName` varchar(255) NOT NULL DEFAULT \'\' COMMENT \'备注信息\' AFTER `anotherColumeName`;

• 修改某个字段：

ALTER TABLE `tableName` MODIFY COLUMN `columeName` DATETIME NOT NULL DEFAULT \'0001-00-00 00:00:00\' COMMENT \'时间\' AFTER `anotherColumeName`;

• 创建表：

CREATE TABLE `tableName` (
  `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
  `msg` varchar(60) NOT NULL DEFAULT \'\' COMMENT \'备注\',
  `create_time` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT \'创建时间\',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT=\'导出excel\';

• 删除数据库
  drop database tableName；

• 删除表
  drop table 表名;

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MySQL5.7以上版本json字段的处理

创建表：

CREATE TABLE `tb_testjson` (
	`id` BIGINT(20) NOT NULL AUTO_INCREMENT,
	`content` JSON NULL DEFAULT NULL,
	PRIMARY KEY (`id`)
)
COLLATE=\'latin1_swedish_ci\'
ENGINE=InnoDB
AUTO_INCREMENT=0
;

1.查询json字段的值

select content ,JSON_EXTRACT(content,"$.name") as name from tb_testjson;

#select content ,content->"$.name" as name from tb_testjson;

2.插入：
UPDATE tb_testjson SET content=JSON_ARRAY_APPEND(content,\'$.name\',\'test\') WHERE id = 2;

{"age": "11", "name": ["ww", "test"]}