release-21.2: norm: do not fold floor division with unit denominator

[msirek]

Backport 1/1 commits from #87808.

/cc @cockroachdb/release

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Fixes #87605

The floor division operator // is like division but drops the
fractional portion of the result. Normalization rule FoldDivOne
rewrites (column // 1) as (column) which is incorrect if the
data in column has fractional digits, as those digits should be
dropped.

The solution is to only fold (column // 1) when column is one of
the integer types.

Release note (bug fix): This patch fixes incorrect results from
the floor division operator, //, when the numerator is non-constant
and the denominator is the constant 1.

Release justification: low risk fix for incorrect results on divide by 1

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Patches should only be created for serious issues or test-only changes.
• Patches should not break backwards-compatibility.
• Patches should change as little code as possible.
• Patches should not change on-disk formats or node communication protocols.
• Patches should not add new functionality.
• Patches must not add, edit, or otherwise modify cluster versions; or add version gates.

If some of the basic criteria cannot be satisfied, ensure that the exceptional criteria are satisfied within.

• There is a high priority need for the functionality that cannot wait until the next release and is difficult to address in another way.
• The new functionality is additive-only and only runs for clusters which have specifically “opted in” to it (e.g. by a cluster setting).
• New code is protected by a conditional check that is trivial to verify and ensures that it only runs for opt-in clusters.
• The PM and TL on the team that owns the changed code have signed off that the change obeys the above rules.

Add a brief release justification to the body of your PR to justify this backport.

Some other things to consider:

• What did we do to ensure that a user that doesn’t know & care about this backport, has no idea that it happened?
• Will this work in a cluster of mixed patch versions? Did we test that?
• If a user upgrades a patch version, uses this feature, and then downgrades, what happens?

[cockroach-teamcity]

This change is 

[DrewKimball]

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @mgartner and @msirek)

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pkg/sql/opt/norm/general_funcs.go line 69 at r1 (raw file):

// IsJSON returns true if the given scalar expression is of type
// JSON.
func (c *CustomFuncs) IsJSON(scalar opt.ScalarExpr) bool {

[nit] Added by the backport

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pkg/sql/logictest/testdata/logic_test/float line 163 at r1 (raw file):

true  false

statement ok

[nit] I think everything above this was added incorrectly by the backport

[msirek]

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @DrewKimball and @mgartner)

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pkg/sql/opt/norm/general_funcs.go line 69 at r1 (raw file):

Previously, DrewKimball (Drew Kimball) wrote…

[nit] Added by the backport

Fixed

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pkg/sql/logictest/testdata/logic_test/float line 163 at r1 (raw file):

Previously, DrewKimball (Drew Kimball) wrote…

[nit] I think everything above this was added incorrectly by the backport

Fixed, thanks.

[rytaft]

Reviewed 3 of 5 files at r1, 2 of 2 files at r2, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @DrewKimball and @mgartner)