sql: fix trigger interaction with computed columns

[DrewKimball]

This commit makes the following changes to the way row-level BEFORE triggers interact with computed columns:

• BEFORE triggers now observe NULL values in place of computed columns.
• Modifications to computed columns by BEFORE triggers are ignored.
• Computed columns are re-computed after row-level BEFORE triggers execute.

These changes make the behavior consistent with that of Postgres.

Fixes #132979

Release note: None

[cockroach-teamcity]

This change is 

[mgartner]

Reviewed all commit messages.
Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @DrewKimball and @mw5h)

---

pkg/sql/opt/optbuilder/trigger.go line 136 at r1 (raw file):

	// the computed columns.
	if eventType == tree.TriggerEventInsert || eventType == tree.TriggerEventUpdate {
		mb.recomputeComputedColsForTrigger(eventType)

I think an optbiulder test or two for this would be useful to show how this recomputation is planned.

---

pkg/sql/opt/optbuilder/trigger.go line 830 at r1 (raw file):

// hasRowLevelTriggers returns true if the table has any row-level triggers that
// match the given action time and event type.
func (mb *mutationBuilder) hasRowLevelTriggers(

This function is not used in this PR - remove it?

---

pkg/ccl/logictestccl/testdata/logic_test/triggers line 2601 at r1 (raw file):

# see NULLs. In addition, while a BEFORE trigger can modify a computed column,
# the changed value is ignored. In contrast, the computed column *does* show
# the effect of modifications to the columns it depends on.

Does a WHEN expression see NULLs for the computed column, or the pre-trigger value of the column? Can you add some tests for this case?

[DrewKimball]

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @mgartner and @mw5h)

---

pkg/sql/opt/optbuilder/trigger.go line 136 at r1 (raw file):

Previously, mgartner (Marcus Gartner) wrote…

I think an optbiulder test or two for this would be useful to show how this recomputation is planned.

Good idea, Done.

---

pkg/sql/opt/optbuilder/trigger.go line 830 at r1 (raw file):

Previously, mgartner (Marcus Gartner) wrote…

This function is not used in this PR - remove it?

🤦 Oops, removed it.

---

pkg/ccl/logictestccl/testdata/logic_test/triggers line 2601 at r1 (raw file):

Previously, mgartner (Marcus Gartner) wrote…

Does a WHEN expression see NULLs for the computed column, or the pre-trigger value of the column? Can you add some tests for this case?

It sees NULLs, I'll add some tests.

[mgartner]

Nicely done!

Reviewed 2 of 3 files at r2, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @mw5h)

[DrewKimball]

TFTR!

bors r+

[craig]

Build failed (retrying...):

• unit_tests

[DrewKimball]

bors r-

[craig]

Canceled.

[DrewKimball]

Needed a rebase.

[mgartner]

bors r+

[craig]

Build succeeded:

• linux_arm64_build
• windows_build
• examples_orms
• macos_amd64_build
• acceptance
• linux_amd64_fips_build
• local_roachtest
• local_roachtest_fips
• unit_tests
• docker_image_amd64
• check_generated_code
• macos_arm64_build
• lint
• linux_amd64_build

[blathers-crl]

Based on the specified backports for this PR, I applied new labels to the following linked issue(s). Please adjust the labels as needed to match the branches actually affected by the issue(s), including adding any known older branches.

---

Issue #132979: branch-release-24.3.

---

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}

[blathers-crl]

Encountered an error creating backports. Some common things that can go wrong:

1. The backport branch might have already existed.
2. There was a merge conflict.
3. The backport branch contained merge commits.

You might need to create your backport manually using the backport tool.

---

error creating merge commit from 43d6d62 to blathers/backport-release-24.3-133328: POST https://api.github.com/repos/cockroachdb/cockroach/merges: 409 Merge conflict []

you may need to manually resolve merge conflicts with the backport tool.

Backport to branch 24.3.x failed. See errors above.

---

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}