How can I set the default value of a datetime field to the time when the inserted value is used during MySQL table creation?

Use the timestamp column type,

Column Type display format
Timestamp (14) yyyymmddhhmmss
Timestamp (12) yymmddhhmmss
Timestamp (10) yymmddhhmm
Timestamp (8) yyyymmdd
Timestamp (6) yymmdd
Timestamp (4) yymm
Timestamp (2) YY


It will automatically mark your insert or update operations with the current date and time. If a table has multiple timestamp columns, only the first one is automatically updated.

In the following cases, MySQL automatically updates the first timestamp column as the current system time.

1. When an insert, update, or load data infile statement does not explicitly specify its value.

(Note that setting an Update column as its existing value does not cause the timestamp column to be updated, because if you set a column as its current value, MySQL ignores the changes for efficiency. See appendix)

2. You explicitly set the timestamp column as null.

3. The timestamp column except the first one can also be set to the current date and time, as long as the column is set to null, or now ().

Example:

Create Table CATV. Call (
Callintime timestamp (14 ),
Calldh varchar (10) default '',
Callnm varchar (10) default '',
Calldq varchar (20) not null default '',
Callinnum varchar (14) default '',
Callinvoice varchar (28) default '',
Recallnum varchar (14) default '',
Pass Enum ('true', 'false') not null default 'false ',
Key callinnum (callinnum ),
Key callintime (callintime)
)

Update call set callintime = callintime, pass = "true"

The previous command sets all the record pass fields in the table to true, while other field values will not change!