Add min(d), max(d) & hash functions: md5(), sha1(), sha256() (#98)

Sources: 

* questdb/questdb#5156
* questdb/questdb#5173

documentation/reference/function/hash.md

@@ -0,0 +1,147 @@
+---
+title: Hash Functions
+sidebar_label: Hash
+description: Hash (md5, sha1 and sha256) SQL functions reference documentation and explanation.
+---
+
+Hash functions generate fixed-size string outputs from variable-length inputs. 
+
+These functions are useful for data integrity verification, checksums, and data anonymization.
+
+## Supported functions
+
+- [`md5()`](#md5) – Generates a 128-bit (32 character) hash value
+- [`sha1()`](#sha1) – Generates a 160-bit (40 character) hash value
+- [`sha256()`](#sha256) – Generates a 256-bit (64 character) hash value
+
+## Function reference
+
+### md5()
+
+Calculates an MD5 hash of the input value and returns it as a hexadecimal string.
+
+**Arguments:**
+- String, varchar, or binary value
+
+**Return value:**
+- A 32-character hexadecimal string representing the MD5 hash
+- NULL if the input is NULL
+
+**Examples:**
+```questdb-sql title="md5() with string input" demo
+SELECT md5('abc');
+-- Returns: '900150983cd24fb0d6963f7d28e17f72'
+
+SELECT md5('');
+-- Returns: 'd41d8cd98f00b204e9800998ecf8427e'
+```
+
+```questdb-sql title="md5() with UTF-8 input" demo
+SELECT md5('Hello, world!');
+-- Returns: '6cd3556deb0da54bca060b4c39479839'
+```
+
+### sha1()
+
+Calculates a SHA1 hash of the input value and returns it as a hexadecimal string.
+
+**Arguments:**
+- String, varchar, or binary value
+
+**Return value:**
+- A 40-character hexadecimal string representing the SHA1 hash
+- NULL if the input is NULL
+
+**Examples:**
+```questdb-sql title="sha1() with string input" demo
+SELECT sha1('abc');
+-- Returns: 'a9993e364706816aba3e25717850c26c9cd0d89d'
+
+SELECT sha1('');
+-- Returns: 'da39a3ee5e6b4b0d3255bfef95601890afd80709'
+```
+
+```questdb-sql title="sha1() with UTF-8 input" demo
+SELECT sha1('Hello, world!');
+-- Returns: '943a702d06f34599aee1f8da8ef9f7296031d699'
+```
+
+### sha256()
+
+Calculates a SHA256 hash of the input value and returns it as a hexadecimal string.
+
+**Arguments:**
+- String, varchar, or binary value
+
+**Return value:**
+- A 64-character hexadecimal string representing the SHA256 hash
+- NULL if the input is NULL
+
+**Examples:**
+```questdb-sql title="sha256() with string input" demo
+SELECT sha256('abc');
+-- Returns: 'ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad'
+
+SELECT sha256('');
+-- Returns: 'e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855'
+```
+
+```questdb-sql title="sha256() with UTF-8 input" demo
+SELECT sha256('Hello, world!');
+-- Returns: '315f5bdb76d078c43b8ac0064e4a0164612b1fce77c869345bfc94c75894edd3'
+```
+
+## Notes and restrictions
+
+### Input handling
+- All hash functions support string, varchar, and binary inputs
+- Empty strings produce a valid hash value
+- NULL inputs always return NULL outputs
+- UTF-8 strings are fully supported
+
+### Thread safety
+- Hash functions are not thread-safe
+- Each function instance maintains its own internal state
+
+### Output characteristics
+- Output is always lowercase hexadecimal
+- Output length is fixed regardless of input size:
+  - MD5: 32 characters
+  - SHA1: 40 characters
+  - SHA256: 64 characters
+
+### Implementation details
+- Uses Java's built-in MessageDigest implementations
+- Supported algorithms are guaranteed to be available on all Java platforms
+- Processes input in a single pass
+
+### Common use cases
+
+#### Data integrity verification
+
+```questdb-sql
+SELECT 
+    filename,
+    sha256(content) = expected_hash as is_valid
+FROM files;
+```
+
+#### Anonymizing sensitive data
+
+```questdb-sql
+SELECT 
+    md5(email) as hashed_email,
+    count(*) as user_count
+FROM users
+GROUP BY hashed_email;
+```
+
+#### Binary data hashing
+
+```questdb-sql
+SELECT 
+    file_id,
+    sha1(binary_content) as content_hash
+FROM binary_files;
+```
+

documentation/reference/function/window.md

@@ -104,6 +104,10 @@ Where:
 
 - [`first_value()`](#first_value) – Retrieves the first value in a window
 
+- [`max()`](#max) – Returns the maximum value within a window
+
+- [`min()`](#min) – Returns the minimum value within a window
+
 - [`rank()`](#rank) – Assigns a rank to rows
 
 - [`row_number()`](#row_number) – Assigns sequential numbers to rows
@@ -520,6 +524,84 @@ SELECT
 FROM trades;
 ```
 
+### max()
+
+In the context of window functions, `max(value)` calculates the maximum value within the set of rows defined by the window frame.
+
+**Arguments:**
+
+- `value`: Any numeric value.
+
+**Return value:**
+
+- The maximum value (excluding null) for the rows in the window frame.
+
+**Description**
+
+When used as a window function, `max()` operates on a "window" of rows defined by the `OVER` clause. The rows in this window are determined by the `PARTITION BY`, `ORDER BY`, and frame specification components of the `OVER` clause.
+
+The `max()` function respects the frame clause, meaning it only includes rows within the specified frame in the calculation. The result is a separate value for each row, based on the corresponding window of rows.
+
+Note that the order of rows in the result set is not guaranteed to be the same with each execution of the query. To ensure a consistent order, use an `ORDER BY` clause outside of the `OVER` clause.
+
+**Syntax:**
+```questdb-sql title="max() syntax" 
+max(value) OVER (window_definition)
+```
+
+**Example:**
+```questdb-sql title="max() example" demo
+SELECT
+    symbol,
+    price,
+    timestamp,
+    max(price) OVER (
+        PARTITION BY symbol
+        ORDER BY timestamp
+        ROWS BETWEEN 3 PRECEDING AND CURRENT ROW
+    ) AS highest_price
+FROM trades;
+```
+
+### min()
+
+In the context of window functions, `min(value)` calculates the minimum value within the set of rows defined by the window frame.
+
+**Arguments:**
+
+- `value`: Any numeric value.
+
+**Return value:**
+
+- The minimum value (excluding null) for the rows in the window frame.
+
+**Description**
+
+When used as a window function, `min()` operates on a "window" of rows defined by the `OVER` clause. The rows in this window are determined by the `PARTITION BY`, `ORDER BY`, and frame specification components of the `OVER` clause.
+
+The `min()` function respects the frame clause, meaning it only includes rows within the specified frame in the calculation. The result is a separate value for each row, based on the corresponding window of rows.
+
+Note that the order of rows in the result set is not guaranteed to be the same with each execution of the query. To ensure a consistent order, use an `ORDER BY` clause outside of the `OVER` clause.
+
+**Syntax:**
+```questdb-sql title="min() syntax" 
+min(value) OVER (window_definition)
+```
+
+**Example:**
+```questdb-sql title="min() example" demo
+SELECT
+    symbol,
+    price,
+    timestamp,
+    min(price) OVER (
+        PARTITION BY symbol
+        ORDER BY timestamp
+        ROWS BETWEEN 3 PRECEDING AND CURRENT ROW
+    ) AS lowest_price
+FROM trades;
+```
+
 ### rank()
 
 In the context of window functions, `rank()` assigns a unique rank to each row

documentation/sidebars.js

@@ -266,6 +266,7 @@ module.exports = {
             "reference/function/conditional",
             "reference/function/date-time",
             "reference/function/finance",
+            "reference/function/hash",
             "reference/function/meta",
             "reference/function/numeric",
             "reference/function/parquet",