Add toMillisecond function

[Blargian]

Closes #54746

Changelog category (leave one):

• New Feature

Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):

Added function toMillisecond which returns the millisecond component for values of typeDateTime or DateTime64.

Documentation entry for user-facing changes

• Documentation is written (mandatory for new features)

[robot-clickhouse]

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[rschu1ze]

@Blargian I made some fixes (including some in related code). The problem with this PR is that the millisecond calculation is wrong. Kindly see my annotations in tests/queries/0_stateless/02998_to_milliseconds.sql for the expected results (basically the millisecond component of the input, similar to what toSecond, toMinute etc. return.

[Blargian]

@Blargian I made some fixes (including some in related code). The problem with this PR is that the millisecond calculation is wrong. Kindly see my annotations in tests/queries/0_stateless/02998_to_milliseconds.sql for the expected results (basically the millisecond component of the input, similar to what toSecond, toMinute etc. return.

@rschu1ze I am probably overlooking something but the Time or UInt64 type seems only to be storing the time since epoch in seconds. For instance toUInt64(toDateTime64('2023-04-21 10:20:30.123', 3)) returns 1682065230 from which the minimum time interval recoverable is only seconds. Is Time not the correct type to be working with here as the input parameter to toMillisecond as it is in toSecond?

[rschu1ze]

That's right, Time or UInt64 isn't sufficient. I did not debug the whole thing, so I can only give some pointers:

• ToDateTimeComponentsImpl in src/Functions/DateTimeTransforms.h shows how to get sub-second components (milliseconds) for values of (SQL) type DateTime64. One basically also needs the scale multiplier for that.
• The code in ToStartOfMillisecondImpl (src/Functions/DateTimeTransforms.h) seems relevant. You could debug what happens in SQL function toStartOfMillisecond() (which however returns a DateTime64 instead of an integer).
• Perhaps it is as easy as adding a new function (similar in spirit to static UInt64 execute(const DateTime64 & datetime64, Int64 scale_multiplier, const DateLUTImpl &) to ToMillisecondImpl which uses the scale_multiplier to determine the result.

[rschu1ze]

Approved (will merge when the tests in CI are green), thanks a lot for taking care!

[tavplubix]

will merge when the tests in CI are green

Well, they are not