Implement current_time scalar function

[naosense]

Which issue does this PR close?

Closes #3982 .

Rationale for this change

DataFusion users need to be able to use the current time to calculate things like "all data in the last 5 hours"

What changes are included in this PR?

Scalar current_time function

Are there any user-facing changes?

[waitingkuo]

LGTM, thank you @naosense

[naosense]

I followed @comphead 's current_date test case

let sql = "select case when current_time() = cast(now() as time) then 'OK' else 'FAIL' end result";
    let results = execute_to_batches(&ctx, sql).await;

    let expected = vec![
        "+--------+",
        "| result |",
        "+--------+",
        "| OK     |",
        "+--------+",
    ];

    assert_batches_eq!(expected, &results);

but it reported an error

thread 'sql::timestamp::test_current_time' panicked at 'called `Result::unwrap()` on an `Err` value: "NotImplemented(\"Unsupported CAST from Timestamp(Nanosecond, Some(\\\"UTC\\\")) to Time64(Nanosecond)\") at Creating physical plan for 'select case when current_time() = cast(now() as time) then 'OK' else 'FAIL' end result': Projection: CASE WHEN currenttime() = CAST(now() AS Time64(Nanosecond)) THEN Utf8(\"OK\") ELSE Utf8(\"FAIL\") END AS result\n  EmptyRelation"', datafusion/core/tests/sql/mod.rs:806:10

Is anything i missed?

[mingmwang]

If there are multiple current_time() in a SQL statement, will it be invoked multiple times or just once ?

[waitingkuo]

casting Timestamp to Time isn't supported in arrow-rs
https://github.com/apache/arrow-rs/blob/master/arrow/src/compute/kernels/cast.rs#L236-L265

[waitingkuo]

@naosense
you can do the following for now if you want to add that test case

❯ select (now()::bigint % 86400000000000)::time;
+-------------------------------+
| now() % Int64(86400000000000) |
+-------------------------------+
| 07:41:27.421667               |
+-------------------------------+

i'll be great if you could fire a issue (or even a pr) to arrow-rs to support cast Timestamp to Time

[waitingkuo]

👍

@mingmwang all the current_time within a query uses the same query_execution_start_time

[waitingkuo]

thank you @naosense

[waitingkuo]

👍

[waitingkuo]

👍

[naosense]

@waitingkuo

i'll be great if you could fire a issue (or even a pr) to arrow-rs to support cast Timestamp to Time

it's a pleasure, I'll investigate how to do that

[alamb]

This looks great @naosense . Thanks @waitingkuo for the review!

[alamb]

Hi @naosense -- it seems this PR needs to have cargo fmt to run on it in order to pass CI. I took the liberty of doing so (and merging up from master) to prevent another 24 hour cycle

[alamb]

Thanks again @naosense and @waitingkuo !

[ursabot]

Benchmark runs are scheduled for baseline = 8c26530 and contender = 97f2e4f. 97f2e4f is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ec2-t3-xlarge-us-east-2] ec2-t3-xlarge-us-east-2
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on test-mac-arm] test-mac-arm
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ursa-i9-9960x] ursa-i9-9960x
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ursa-thinkcentre-m75q] ursa-thinkcentre-m75q
Buildkite builds:
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python, R. Runs only benchmarks with cloud = True
test-mac-arm: Supported benchmark langs: C++, Python, R
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java