From 90d4e1325c982dca01605c50b847bbc49d1c2802 Mon Sep 17 00:00:00 2001
From: codeAnqiang-ma <273298913+codeAnqiang-ma@users.noreply.github.com>
Date: Thu, 13 Aug 2026 19:59:37 +0800
Subject: [PATCH] docs: fix signum documentation to say zero returns 0
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The `#[user_doc]` description for `signum` said "Zero and positive numbers
return `1`", but `signum(0)` returns `0`. The repository's own tests already
assert this: scalar.slt checks `select signum(-2), signum(0), signum(2);`
returns `-1 0 1`, and the signum unit tests assert `signum(±0.0) == 0.0`.

That behavior is intentional and matches PostgreSQL `sign()` and Spark
`signum()`; it was changed on purpose in #11580 (issue #11557). Only the
documentation was left describing the old behavior, so this updates the
description and regenerates docs/source/user-guide/sql/scalar_functions.md
with dev/update_function_docs.sh. No behavior change.

Assisted-by: Cursor (Opus 5)
---
 datafusion/functions/src/math/signum.rs        | 3 ++-
 docs/source/user-guide/sql/scalar_functions.md | 3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/datafusion/functions/src/math/signum.rs b/datafusion/functions/src/math/signum.rs
index 05b78fcffe2a7..21b38988c0a01 100644
--- a/datafusion/functions/src/math/signum.rs
+++ b/datafusion/functions/src/math/signum.rs
@@ -34,7 +34,8 @@ use datafusion_macros::user_doc;
     doc_section(label = "Math Functions"),
     description = r#"Returns the sign of a number.
 Negative numbers return `-1`.
-Zero and positive numbers return `1`."#,
+Zero returns `0`.
+Positive numbers return `1`."#,
     syntax_example = "signum(numeric_expression)",
     standard_argument(name = "numeric_expression", prefix = "Numeric"),
     sql_example = r#"```sql
diff --git a/docs/source/user-guide/sql/scalar_functions.md b/docs/source/user-guide/sql/scalar_functions.md
index 1bfec4ce43599..644d42935ec29 100644
--- a/docs/source/user-guide/sql/scalar_functions.md
+++ b/docs/source/user-guide/sql/scalar_functions.md
@@ -796,7 +796,8 @@ round(numeric_expression[, decimal_places])
 
 Returns the sign of a number.
 Negative numbers return `-1`.
-Zero and positive numbers return `1`.
+Zero returns `0`.
+Positive numbers return `1`.
 
 ```sql
 signum(numeric_expression)