opt: prevent columns reuse in Union and UnionAll

[mgartner]

opt: fix columns in SplitScanIntoUnionScans constraint

This commit fixes a minor bug in SplitScanIntoUnionScans that resulted
in a scan's constraint containing columns not associated with the scan.
This did not affect the correctness of results. However it appears that
it did cause inaccurate stats calculations; I had to add histogram
buckets to the tests to coerce the optimizer into choosing the same
plan for the corresponding test.

Release note: None

opt: do not reuse columns for Unions in SplitScanIntoUnionScans

Unions generated in SplitScanIntoUnionScans no longer reuse column IDs
from their left children as output column IDs. Reusing column IDs in
this way has shown to be dangerous (see #58434).

Release note: None

opt: add Union column ID check to CheckExpr

A check has been added to CheckExpr that asserts that the output
columns of Unions and UnionAlls are not reused from the left or
right inputs of the union. Reusing columns in this way is dangerous
(see #58434).

Release note: None

[cockroach-teamcity]

This change is 

[mgartner]

cc @DrewKimball: in case you want to take a look at this

[rytaft]

Reviewed 2 of 2 files at r1, 5 of 5 files at r2, 1 of 1 files at r3.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @andy-kimball, @mgartner, and @RaduBerinde)

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pkg/sql/opt/xform/limit_funcs.go, line 252 at r2 (raw file):

	// makeNewUnion extends the Union tree rooted at 'last' to include 'newScan'.
	// The ColumnIDs of the original Scan are used by the resulting expression.
	//oldColList := scan.Relational().OutputCols.ToList()

dead code

---

pkg/sql/opt/xform/limit_funcs.go, line 290 at r2 (raw file):

			// Add the scan to the union tree. If it is the final union in the
			// tree, use the original scan's columns as the union's out columns.
			// Otherwise, created new output column IDs for the union.

created -> create

---

pkg/sql/opt/xform/testdata/rules/limit, line 92 at r1 (raw file):

    "null_count": 0,
    "histo_col_type": "int",
    "histo_buckets": [

[nit] the histogram row count adds up to more than the row count above.

(I've been meaning to add some histogram validation into our testutils but haven't done it yet)

[mgartner]

Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @andy-kimball, @RaduBerinde, and @rytaft)

---

pkg/sql/opt/xform/limit_funcs.go, line 252 at r2 (raw file):

Previously, rytaft (Rebecca Taft) wrote…

dead code

Done.

---

pkg/sql/opt/xform/limit_funcs.go, line 290 at r2 (raw file):

Previously, rytaft (Rebecca Taft) wrote…

created -> create

Done.

---

pkg/sql/opt/xform/testdata/rules/limit, line 92 at r1 (raw file):

Previously, rytaft (Rebecca Taft) wrote…

[nit] the histogram row count adds up to more than the row count above.

(I've been meaning to add some histogram validation into our testutils but haven't done it yet)

1000 + 1000 + 998000 = 1000000 What am I missing?

[rytaft]

Reviewed 2 of 2 files at r4, 1 of 1 files at r5.
Reviewable status: complete! 0 of 0 LGTMs obtained (and 1 stale) (waiting on @andy-kimball and @RaduBerinde)

---

pkg/sql/opt/xform/testdata/rules/limit, line 92 at r1 (raw file):

Previously, mgartner (Marcus Gartner) wrote…

1000 + 1000 + 998000 = 1000000 What am I missing?

Oh sorry I got confused -- I thought the 2000 was num_eq not upper_bound. Ignore me!

[mgartner]

No worries! TFTR.

bors r=rytaft

[craig]

Build failed:

• GitHub CI (Cockroach)

[mgartner]

bors r=rytaft

[craig]

Build succeeded:

• GitHub CI (Cockroach)