Why do PostgreSQL and MySQL date accuracy only to microseconds?

Question

MySQL

Date storage accuracy in different relational databases is different:

+--------------+-------------------------------+----------------+
| Oracle       | 2001-01-01 23:59:59:999999999 | наносекунда    |
| MSSQL        | 2001-01-01 23:59:59:9999999   | сто наносекунд |
| MySQL        | 2001-01-01 23:59:59:999999    | микросекунда   |
| PostgreSQL   | 2001-01-01 23:59:59:999999    | микросекунда   |
+--------------+-------------------------------+----------------+

What prevents MSSQL, MySQL, PostgreSQL from maintaining date accuracy up to nanoseconds, like Oracle?

Answer 1

Increased accuracy requires increased resource costs.
For most users, such accuracy is not needed, and if the need arises, then it can be implemented in an alternative way, for example, by storing these extra values ​​in a separate table field.

Answer 2

What prevents MSSQL from maintaining nanosecond date precision

The fact that in Windows all the built-in timestamps have an accuracy of 100ns. Because the FILETIME data format is an integer number of hundreds of nanoseconds since the year 1601.

Answer 3

In Delphi, the normal solution is the integer part: Years from where, the fractional part Time - according to the Delphic concepts Float. How exactly...