[SPARK-27878][SQL] Support ARRAY(subquery) expressions

[peter-toth]

What changes were proposed in this pull request?

This PR adds support for array creation from subquery so this example becomes valid:

select array(select c from t)

How was this patch tested?

Added new UTs.

[SparkQA]

Test build #107542 has finished for PR 25118 at commit fcef61e.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):
• case class ArraySubquery(

[maropu]

Is this syntax supported in the other DBMSs, e.g., mysql and oracle? (I know pg accepts this one though)

[peter-toth]

I found only BigQuery that supports it: https://cloud.google.com/bigquery/docs/reference/standard-sql/arrays#creating-arrays-from-subqueries

[maropu]

If so, I think it has a lower priority to support this syntax .... (cuz we already have the other higher priority issues you know...)

[peter-toth]

If so, I think it has a lower priority to support this syntax .... (cuz we already have the other higher priority issues you know...)

Ok, got it. I keep this PR open though.

[maropu]

Thanks. This is just my opinion and the other developers might not think so. Its ok to keep it open for a while.

[github-actions]

We're closing this PR because it hasn't been updated in a while.
This isn't a judgement on the merit of the PR in any way. It's just
a way of keeping the PR queue manageable.

If you'd like to revive this PR, please reopen it!

[HyukjinKwon]

Yeah, I think we shouldn't support this case for now but thanks for your contribution and analysis, @peter-toth .