update string CHAR func (#2421)

Author: BohuTANG

docs/en/sql-reference/20-sql-functions/06-string-functions/char.md

@@ -3,32 +3,82 @@ id: string-char
 title: CHAR
 ---
 
-Return the character for each integer passed.
+import FunctionDescription from '@site/src/components/FunctionDescription';
+
+<FunctionDescription description="Introduced or updated: v1.2.752"/>
+
+
+Returns the character(s) for each integer passed. The function converts each integer to its corresponding Unicode character.
 
 ## Syntax
 
 ```sql
 CHAR(N, ...)
+CHR(N)
 ```
 
 ## Arguments
 
-| Arguments | Description    |
-|-----------|----------------|
-| N         | Numeric Column |
+| Arguments | Description                                                    |
+|-----------|----------------------------------------------------------------|
+| N         | Integer value(s) representing Unicode code points (0 to 2^32-1) |
 
 ## Return Type
 
-`BINARY`
+`STRING`
+
+## Remarks
+
+- Accepts any integer type (auto-casts to Int64).
+- Returns empty string ('') and logs an error for invalid code points.
+- `chr` is an alias for `char`.
+- NULL inputs result in NULL output.
 
 ## Examples
 
 ```sql
-SELECT CHAR(77,121,83,81,76) as a, a::String;
-┌────────────────────────┐
-│      a     │ a::string │
-│   Binary   │   String  │
-├────────────┼───────────┤
-│ 4D7953514C │ MySQL     │
-└────────────────────────┘
+-- Basic usage
+SELECT CHAR(65, 66, 67);
+┌───────┐
+│ char  │
+│ String│
+├───────┤
+│ ABC   │
+└───────┘
+
+-- Using the CHR alias
+SELECT CHR(68);
+┌───────┐
+│ chr   │
+│ String│
+├───────┤
+│ D     │
+└───────┘
+
+-- Creating a string from multiple code points
+SELECT CHAR(77,121,83,81,76);
+┌───────┐
+│ char  │
+│ String│
+├───────┤
+│ MySQL │
+└───────┘
+
+-- Auto-casting from different integer types
+SELECT CHAR(CAST(65 AS UInt16));
+┌───────┐
+│ char  │
+│ String│
+├───────┤
+│ A     │
+└───────┘
+
+-- NULL handling
+SELECT CHAR(NULL);
+┌───────┐
+│ char  │
+│ String│
+├───────┤
+│ NULL  │
+└───────┘
 ```

docs/en/sql-reference/20-sql-functions/06-string-functions/index.md

@@ -87,7 +87,7 @@ This page provides a comprehensive overview of String functions in Databend, org
 |----------|-------------|---------|
 | [ASCII](ascii.md) | Returns ASCII value of first character | `ASCII('D')` → `68` |
 | [ORD](ord.md) | Returns Unicode code point of first character | `ORD('D')` → `68` |
-| [CHAR](char.md) | Returns character for given code points | `CHAR(68,97,116,97)` → `'Data'` |
+| [CHAR](char.md) / [CHR](char.md) | Returns string of characters for given Unicode code points | `CHAR(68,97,116,97)` → `'Data'` |
 | [BIN](bin.md) | Returns binary representation | `BIN(5)` → `'101'` |
 | [OCT](oct.md) | Returns octal representation | `OCT(8)` → `'10'` |
 | [HEX](hex.md) | Returns hexadecimal representation | `HEX('ABC')` → `'414243'` |