sql: Add support for numeric JSON scalar casts

[chrisseto]

• Fixes sql: support missing JSON numeric scalar casts #41333
• Add support for queries such as
  • SELECT '1'::jsonb::int
  • SELECT '1'::jsonb::float
  • SELECT '3.14'::jsonb::decimal

Release note (sql change): Casting JSON numeric scalars to numeric
types now works as expected.

[cockroach-teamcity]

This change is 

[justinj]

Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @chrisseto)

---

pkg/sql/sem/tree/eval.go, line 3219 at r1 (raw file):

			if v.Type() == json.NumberJSONType {
				// err is ignored as a more appropriate error
				// will be generated later

nit: periods on comments (same below)

also, if we're always(?) just going to ignore this error, can we just not construct it in the first place and return a bool indicating whether we were able to successfully do the conversion?

---

pkg/sql/sem/tree/testdata/eval/cast, line 1034 at r1 (raw file):

'3.14'::jsonb::string
----
'3.14'

nit: this could include some invalid cases, and also some that invoke truncation(?) like '1.5'::json::int (should compare to postgres to determine the proper behaviour).

---

pkg/util/json/json.go, line 975 at r1 (raw file):

}

// ToDecimal returns a apd.Decimal given a JSON value

nit: "...an apd.Decimal..." and period at the end of comment

[jordanlewis]

Hey @chrisseto, any interest in finishing this fella up?

[chrisseto]

@jordanlewis Hey! Sorry for the late response but yes I am. I ran into some issues with decimals IIRC.
Would you mind if I stole a bit of your time on a Friday?

[jordanlewis]

Let's do it!

[nvanbenschoten]

This PR looks great! I've always found the ergonomics of JSON to be a little off, and I think a lot of it has to do with the absence of these casts. @chrisseto any plans to polish this off and get it merged?

[chrisseto]

Thanks for the ping @nvanbenschoten. I'll see if I can get it cleaned up this week!

[jordanlewis]

cc @rafiss

[rafiss]

this lgtm! thanks @chrisseto! looks it does need a rebase though

[rafiss]

awesome!

bors r+

[chrisseto]

TFRT @rafiss !!

[craig]

Build succeeded:

• GitHub CI (Cockroach)