fix issue with now() returning same value across statements

[kmitchener]

Which issue does this PR close?

Closes #3057 .

Rationale for this change

What changes are included in this PR?

Root cause of the issue was that down one code path, creating a physical plan wasn't setting the query_execution_start_time in session state. I've fixed it by making the code the same between DataFrame's create_physical_plan() and SessionContext's create_physical_plan().

• I added tests to ensure now() returns a consistent value within a statement but different values when called in different statements within the same SessionContext. I added tests for SQL and using the DataFrame API to ensure it works via the different code paths for collecting dataframes.
• views are fixed so that they return now() properly
  • a side-effect of this is that we now store unoptimized plans in view definitions and optimize it on every view execution. I believe this is preferable behavior anyway and also don't see any other way to have now() or functions like that work in views.
• Some functions are incorrectly declared as unary #3069 is partially resolved .. needed to fix the now() expression definition here

I'm still not that happy with how I solved it the root issue with the SessionState cloning via this code duplication, but can follow up with a separate PR.

Are there any user-facing changes?

now() works correctly across statements in the same session regardless of code path taken to execute the SQL

[codecov-commenter]

Codecov Report

Merging #3210 (c95326a) into master (3df9f80) will decrease coverage by 0.00%.
The diff coverage is 96.55%.

@@            Coverage Diff             @@
##           master    #3210      +/-   ##
==========================================
- Coverage   85.85%   85.85%   -0.01%     
==========================================
  Files         291      291              
  Lines       52899    52938      +39     
==========================================
+ Hits        45416    45448      +32     
- Misses       7483     7490       +7     

Impacted Files	Coverage Δ
datafusion/core/src/physical_plan/mod.rs	88.00% <ø> (ø)
...tafusion/physical-expr/src/datetime_expressions.rs	83.52% <ø> (ø)
datafusion/proto/src/from_proto.rs	35.40% <0.00%> (+0.12%)	⬆️
datafusion/core/tests/sql/timestamp.rs	99.65% <97.82%> (-0.17%)	⬇️
datafusion/core/src/dataframe.rs	88.91% <100.00%> (+0.05%)	⬆️
datafusion/core/src/datasource/view.rs	87.06% <100.00%> (+0.22%)	⬆️
datafusion/core/src/execution/context.rs	78.18% <100.00%> (-0.06%)	⬇️
datafusion/expr/src/expr_fn.rs	91.06% <100.00%> (+0.05%)	⬆️
datafusion/expr/src/window_frame.rs	92.43% <0.00%> (-0.85%)	⬇️
.../physical-expr/src/aggregate/array_agg_distinct.rs	79.41% <0.00%> (-0.78%)	⬇️
... and 15 more

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[andygrove]

LGTM. Thanks @kmitchener.

Bonus points if you could put a brief description in the user guide for now() while you are here, in the SQL scalar function reference.

[kmitchener]

Good thinking, docs updated.

[kmitchener]

Actually, I'm going to make this a WIP because I tested with a now() in a view and that code path is still broken. Needs a more robust fix. Will pick it up again in a couple days.

[liukun4515]

Actually, I'm going to make this a WIP because I tested with a now() in a view and that code path is still broken. Needs a more robust fix. Will pick it up again in a couple days.

You can convert this pr as a draft @kmitchener If there are some bug or issue not resolved

[kmitchener]

@andygrove PTAL

[andygrove]

LGTM, but I think one test needs to be added. See earlier comment.

[ursabot]

Benchmark runs are scheduled for baseline = c72f547 and contender = eedc787. eedc787 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

[alamb]

Thank you for thisPR @kmitchener 👍