2021
Olaf Dietsche's answer is right but old (2012) & slightly inaccurate as of 2021. According to Wikipedia ISO 8601:
As of ISO 8601-1:2019, the basic format is T[hh][mm][ss] and the
extended format is T[hh]:[mm]:[ss]. Earlier versions omitted the T
(representing time) in both formats.
Also from same link:
ISO 8601-1:2019 allows the T to be omitted in the extended format, as
in "13:47:30", but only allows the T to be omitted in the basic format
when there is no risk of ambiguity with date expressions.
MySQL in their documentation mention "ISO" (with no number), in one link they did mention that ISO format refers to ISO 9075, not ISO 8601.
.
ISO 9075 is basically MySQL standards.
btw, ISO 8601 & RFC 3339 are pretty much the same thing (from developers' perspective). In case you are interested, read.
Bottom line:
MySQL datetime format matches same format of ISO-8601 / RFC-3339 , although MySQL has its own standard ISO 9075. So, for the MySQL datetime format, we can refer to it as any of the below:
- ISO 8601 aka RFC 3339
- MySQL format aka ISO 9075.