sql: Add support for JOIN LATERAL syntax

[chrisseto]

As correlated subqueries are already supported, only minor scoping
changes are required to fully support Postgres' JOIN LATERAL syntax.

h/t @justinj for the support

Release note (sql change): Adds support for JOIN LATERAL syntax.

[cockroach-teamcity]

This change is 

[justinj]

🎉 awesome!! couple nit things

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @chrisseto, @justinj, @RaduBerinde, and @rytaft)

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pkg/sql/logictest/testdata/logic_test/subquery_correlated, line 1177 at r1 (raw file):

query ITT rowsort
SELECT
	c_id, bill, states

nit: spaces over tabs, if you use sqlfmt you can add the --use-spaces flag to enforce this, I have this in my vimrc to sqlfmt whatever I have visually selected:

noremap ,s :!cockroach sqlfmt --print-width 80 --use-spaces<cr><cr>

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pkg/sql/opt/optbuilder/join.go, line 37 at r1 (raw file):

	isLateral := false
	inScopeRight := inScope
	// Detect if this is a lateral join, upgrade scope to leftScope need be

nit: if need be? also our style guide requires periods at the end of comments

maybe also worth including in the comment something like "the right side of a LATERAL join has in scope the columns produced from the left side" to make explicit why we have to do this?

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pkg/sql/opt/optbuilder/join.go, line 370 at r1 (raw file):

		jb.filters,
		&memo.JoinPrivate{Flags: jb.joinFlags},
		false,

nit: false /* isLateral */,

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pkg/sql/opt/optbuilder/testdata/lateral, line 292 at r1 (raw file):

build
SELECT * FROM x JOIN LATERAL (SELECT * FROM y WHERE b = x.a) ON true

probably should also test LEFT JOIN LATERAL, and we might also need to error appropriately on use of OUTER JOIN LATERAL and RIGHT JOIN LATERAL (I assume we just let those through at the moment)

[rytaft]

after you address @justinj's comments

Reviewed 3 of 3 files at r1.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @chrisseto and @RaduBerinde)

[chrisseto]

Feedback addressed!
Full disclosure: The actual error from Postgres is

ERROR:  42P10: invalid reference to FROM-clause entry for table "users"
LINE 1: ...ray_agg(code) FROM user_promo_codes WHERE user_id=users.id) ...
                                                             ^
DETAIL:  The combining JOIN type must be INNER or LEFT for a LATERAL reference.
LOCATION:  check_lateral_ref_ok, parse_relation.c:452

I went with detail message and the syntax code as it seemed more appropriate.
Happy to change it if the other is preferred, I may need some pointers on how to generate it.

[justinj]

with some nits, though reminder that this can't be merged until post-20.1-branching.

Reviewable status: complete! 1 of 0 LGTMs obtained (and 1 stale) (waiting on @chrisseto, @RaduBerinde, and @rytaft)

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pkg/sql/opt/optbuilder/join.go, line 201 at r2 (raw file):

	case sqlbase.RightOuterJoin:
		if isLateral {
			panic(pgerror.New(pgcode.Syntax, "The combining JOIN type must be INNER or LEFT for a LATERAL reference."))

nit: hoist this error object into a top-level var (like this) and omit the period in the error message (i think lint will complain about the period)

[rytaft]

Reviewed 1 of 3 files at r2, 2 of 2 files at r3.
Reviewable status: complete! 1 of 0 LGTMs obtained (and 1 stale) (waiting on @chrisseto and @RaduBerinde)

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pkg/sql/opt/optbuilder/join.go, line 181 at r3 (raw file):

}

var invalidLateralJoin = pgerror.New(pgcode.Syntax, "The combining JOIN type must be INNER or LEFT for a LATERAL reference")

[nit] Is this the error Postgres uses? The word "combining" seems unnecessary here and is a bit confusing. I'd just say "The JOIN type must be..."

[rytaft]

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pkg/sql/opt/optbuilder/join.go, line 181 at r3 (raw file):

Previously, rytaft (Rebecca Taft) wrote…

[nit] Is this the error Postgres uses? The word "combining" seems unnecessary here and is a bit confusing. I'd just say "The JOIN type must be..."

Never mind just saw your update above

[justinj]

Now that we've branched I think this is good to go after a rebase!

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

[chrisseto]

bors r+

[craig]

Build failed (retrying...)

• GitHub CI (Cockroach)

[chrisseto]

bors r+

[craig]

Build succeeded

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