mysql automatically adds creation time and update time

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1 Description

In mysql, when the column type in the added table is the time type (timestamp), the default value can be set

Set the default value of the time column to automatically get the creation time:

 default CURRENT_TIMESTAMP

Set the default value of the time column to get the update time automatically:

 default CURRENT_TIMESTAMP on update CURRENT_TIMESTAMP

Add another value that cannot be null

#Create timenot null default CURRENT_TIMESTAMP# update timenot null default CURRENT_TIMESTAMP on update CURRENT_TIMESTAMP

2 full operational SQL

2.1 Modify the default value of the time column in the existing table to be obtained automatically

Modify the create_time column in the table t_user to set the current system time if the value is empty when inserting new data

#Modify the create_time column in the table t_user When inserting new data, if the value is empty, it will be set to the current system timeALTER TABLE t_user MODIFY create_time TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT 'create time';

Modify the update_time column in the table t_user and set the current system time if the value is empty when modifying the data

#Modify the update_time column in the table t_user When modifying the data, if the value is empty, it will be set to the current system timeALTER TABLE t_user MODIFY update_time timestamp not null default CURRENT_TIMESTAMP on update CURRENT_TIMESTAMP COMMENT 'Update time';

2.2 Add a time column to an existing table to set the default value

Add create_time column in table t_user

#Add create_time column in table t_userALTER TABLE t_user ADD create_time timestamp not null default CURRENT_TIMESTAMP COMMENT 'create time';

Add update_time column in table t_user

 #Add update_time column in table t_userALTER TABLE t_user ADD update_time timestamp not null default CURRENT_TIMESTAMP on update CURRENT_TIMESTAMP COMMENT 'Update time';

2.3 Set the default value of the time column when creating a table

create table t_user(id integer not null auto_increment primary key,user_name varchar(20) not null ,update_time timestamp default CURRENT_TIMESTAMP on update CURRENT_TIMESTAMP COMMENT 'Update time',create_time timestamp default CURRENT_TIMESTAMP COMMENT 'create time');

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