CURRENT TIMESTAMP combines CURRENT DATE and CURRENT TIME to form a TIMESTAMP value containing the year, month, day, hour, minute, second and fraction of a second. The fraction of a second is stored to 3 decimal places. The accuracy is limited by the accuracy of the system clock.
Unlike DEFAULT TIMESTAMP, columns declared with DEFAULT CURRENT TIMESTAMP do not necessarily contain unique values. If uniqueness is required, consider using DEFAULT TIMESTAMP instead.
The information CURRENT TIMESTAMP returns is equivalent to the information returned by the GETDATE and NOW functions.
CURRENT_TIMESTAMP is equivalent to CURRENT TIMESTAMP.
The main difference between DEFAULT CURRENT TIMESTAMP and DEFAULT TIMESTAMP is that DEFAULT CURRENT TIMESTAMP is set only at INSERT, while DEFAULT TIMESTAMP is set at both INSERT and UPDATE.