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For columns with the DATE, TIME, or TIMESTAMP data type, you can use the current date, current time, or current timestamp as a default. The default you choose must be compatible with the column's data type.
A current date default might be useful to record:
dates of phone calls in a contacts database
dates of orders in a sales entry database
the date a patron borrows a book in a library database
The current timestamp is similar to the current date default, but offers greater accuracy. For example, a user of a contact management application may have several interactions with a single customer in one day: the current timestamp default would be useful to distinguish these contacts.
Since it records a date and the time down to a precision of millionths of a second, you may also find the current timestamp useful when the sequence of events is important in a database.
The default timestamp provides a way of indicating when each row in the table was last modified. When a column is declared with DEFAULT TIMESTAMP, a default value is provided for inserts, and the value is updated with the current date and time whenever the row is updated. To provide a default value on insert, but not update the column whenever the row is updated, use DEFAULT CURRENT TIMESTAMP instead of DEFAULT TIMESTAMP. See the DEFAULT clause in CREATE TABLE statement.
For more information about timestamps, times, and dates, see SQL Data Types.