DateTime64 parsing goes wrong for string representing a number smaller than 10000:

select toDateTime64('9999', 3)       -- returns 1970-01-01 00:00:00.000, but CANNOT_PARSE_DATETIME expected
select toDateTime64('10000', 3)     -- returns 1970-01-01 02:46:40.000 (expected)

However, DateTime doesn't have this:

select toDateTime('9999');  -- { serverError CANNOT_PARSE_DATETIME } (expected)
select toDateTime('10000')              -- returns 1970-01-01 02:46:40 (expected)

See fiddle.

Does it reproduce on recent release?
Yes, on 23.6.1
Also happens on older versions, e.g. 22.6.7

Expected behavior

DateTime64 shall not silently produce wrong result. It shall throw exception like DateTime does.

Related to these two comments.

Parts:

• fix parsing of decimal string numbers with short whole part (e.g. '123.12') -- definitely no ambiguity here
• allow negative numbers in short strings for DT64 -- also no ambiguity