What does the number 6 in the MySQL DATETIME field mean?

Question

I can't find it in DATETIME, but usually I define it as DATETIME without precision specifier.

When running Hibernate automatic DDL update, I noticed that it changes the table to DATETIME(6)

Answer 1

It represents the precision of millisecond storage.

DATETIME(6) means that decimal milliseconds are stored to 6 decimal places. For example, 1970-01-01 17:51:04.789463.

The number must be in the range between 0 and 6.

Answer 2

This is explained in detail on the next page of the table of contents (emphasis mine):

• So DATETIME is equivalent to DATETIME(0).
• And DATETIME(6) is not equivalent to DATETIME or DATETIME(0).