Fix EXPLAIN around Char and Varchar #31533

ggevay · 2025-02-18T15:57:35Z

Char and Varchar can involve a length. Additionally, the cast functions text_to_char and text_to_varchar involve a fail_on_len option. We were not printing these extra fields in EXPLAIN and in error msgs, causing confusion in various situations, e.g.,
https://github.com/MaterializeInc/database-issues/issues/8807#issuecomment-2518662460
https://github.com/MaterializeInc/database-issues/issues/1291
#27029

The first commit attends to text_to_varchar and text_to_char.

The second commit attends to the type names, changing them in EXPLAIN, error msgs, and pg_typeof.

The third commit reverts the change for pg_typeof, to keep Postgres compatibility.

Nightly: https://buildkite.com/materialize/nightly/builds/11207

Motivation

This PR fixes a recognized bug: https://github.com/MaterializeInc/database-issues/issues/8975

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Checklist

This PR has adequate test coverage / QA involvement has been duly considered. (trigger-ci for additional test/nightly runs)
This PR has an associated up-to-date design doc, is a design doc (template), or is sufficiently small to not require a design.
If this PR evolves an existing $T ⇔ Proto$T mapping (possibly in a backwards-incompatible way), then it is tagged with a T-proto label.
If this PR will require changes to cloud orchestration or tests, there is a companion cloud PR to account for those changes that is tagged with the release-blocker label (example).
If this PR includes major user-facing behavior changes, I have pinged the relevant PM to schedule a changelog post.

ggevay · 2025-02-18T17:09:14Z

There is a problem: The output of pg_typeof is changing with this PR, e.g. from

character varying

to

varchar(1)

This might be a problem, because maybe some external tools rely on these being exactly what Postgres says. In that case, I'll have to separate the pg_typeof code path from the EXPLAIN code path. I'll ask the SQL council.

ggevay · 2025-02-18T17:29:33Z

Will tweak the PR to not change pg_typeof. Council discussion.

mgree

Looks good to me. I like the new, clearer output. There's some risk of using non postgres_compat output in error messages leading people to get confused about type names. Not a huge risk, likely better this way.

mgree · 2025-02-19T17:19:57Z

src/expr/src/scalar/func/impls/string.rs

+                    self.fail_on_len
+                )
+            }
+            None => f.write_str("text_to_char[len=None]"),


The None is a Rust-ism:

Suggested change

None => f.write_str("text_to_char[len=None]"),

None => f.write_str("text_to_char[len=unbounded]"),

Thanks, unbounded is indeed better!

src/expr/src/scalar/func/impls/string.rs

mgree · 2025-02-19T17:23:11Z

src/sql/src/func.rs

                    Ok(elem_type) => elem_type,
                    Err(elem_type) => bail_unsupported!(
-                        format!("array_fill on {}", ecx.humanize_scalar_type(&elem_type))
+                        format!("array_fill on {}", ecx.humanize_scalar_type(&elem_type, false))


Suggested change

format!("array_fill on {}", ecx.humanize_scalar_type(&elem_type, false))

// This will be used in error msgs, therefore we call with `postgres_compat` false.

format!("array_fill on {}", ecx.humanize_scalar_type(&elem_type, false))

... and probably similar at other uses.

Changed this one. Generally, I didn't add this comment to all call sites, only to those where it was not immediately clear whether it's only used in an error msg.

mgree · 2025-02-19T17:27:41Z

test/sqllogictest/char.slt

 # Fixes database-issues#5222

-query error db error: ERROR: coalesce could not convert type "char" to character
+query error db error: ERROR: coalesce could not convert type "char" to char


Oof, tough error message!

Yeah, life is just harsh! :D

But one thing we could possibly do here is to print it more verbosely when postgres_compat is off. For example, we could print it as "char" aka PgLegacyChar. See this comment. What do you think @mgree ?

Sorry to miss this. I think we can let it be confusing for now.

Ok. We can do it in a follow-up PR if we think so later.

test/sqllogictest/github-5536.slt

test/testdrive/char-varchar-distinct.td

SQL council discussion with Marta: https://materializeinc.slack.com/archives/C063H5S7NKE/p1739899659699649?thread_ts=1739898930.961779&cid=C063H5S7NKE

ggevay · 2025-02-20T11:21:56Z

Thanks for the review! Merging.

If we decide to do something about the could not convert type "char" to char error msg, then I'll open a follow-up PR for that.

(The Nightly failure is unrelated.)

ggevay requested review from a team as code owners February 18, 2025 15:57

ggevay requested a review from ParkMyCar February 18, 2025 15:57

ggevay added the A-CLUSTER Topics related to the CLUSTER layer label Feb 18, 2025

ggevay changed the title ~~Fix EXPLAIN around Char Varchar~~ Fix EXPLAIN around Char and Varchar Feb 18, 2025

ggevay marked this pull request as draft February 18, 2025 17:09

ggevay force-pushed the char-varchar-printing branch 3 times, most recently from 3defdae to a846d48 Compare February 19, 2025 13:10

ggevay marked this pull request as ready for review February 19, 2025 13:53

ggevay requested a review from mgree February 19, 2025 14:59

mgree approved these changes Feb 19, 2025

View reviewed changes

ggevay added 4 commits February 19, 2025 19:11

Fix text_to_varchar and text_to_char EXPLAIN printing

8f53e03

Fix char and varchar typename printing in EXPLAIN and error msgs

4a24290

Revert char/varchar printing in pg_typeof

1b69c4c

SQL council discussion with Marta: https://materializeinc.slack.com/archives/C063H5S7NKE/p1739899659699649?thread_ts=1739898930.961779&cid=C063H5S7NKE

Print char/varchar None length as unbounded

377a61e

ggevay force-pushed the char-varchar-printing branch from a846d48 to 377a61e Compare February 20, 2025 11:19

ggevay enabled auto-merge February 20, 2025 11:21

ggevay merged commit c962d78 into MaterializeInc:main Feb 20, 2025
80 checks passed

	None => f.write_str("text_to_char[len=None]"),
	None => f.write_str("text_to_char[len=unbounded]"),

	format!("array_fill on {}", ecx.humanize_scalar_type(&elem_type, false))
	// This will be used in error msgs, therefore we call with `postgres_compat` false.
	format!("array_fill on {}", ecx.humanize_scalar_type(&elem_type, false))

Fix EXPLAIN around Char and Varchar #31533

Fix EXPLAIN around Char and Varchar #31533

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ggevay commented Feb 18, 2025

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ggevay commented Feb 18, 2025 •

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ggevay commented Feb 20, 2025 •

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