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SQL UDF (User Defined Function) Example

This project demonstrates how to create SQL User Defined Functions (UDF) for ArkFlow using Rust. This example implements a simple add_one function that takes an Int64 type input and returns the result of adding 1 to that value.

Project Overview

User Defined Functions (UDF) allow you to extend SQL functionality, implementing custom logic that standard SQL functions cannot directly provide. In this example, we demonstrate how to:

  • Create a simple UDF function
  • Register the function to the ArkFlow processing engine
  • Use the function in SQL queries

Dependencies

This project depends on the following libraries:

  • arkflow-core - ArkFlow core library
  • arkflow-plugin - ArkFlow plugin system
  • datafusion - High-performance query engine for SQL processing
  • tokio - Asynchronous runtime

Code Analysis

Function Implementation

fn add_one(args: &[ColumnarValue]) -> Result<ColumnarValue> {
    // Convert parameters to arrays
    let args = ColumnarValue::values_to_arrays(args)?;
    let i64s = as_int64_array(&args[0])?;

    // Add 1 to each element
    let new_array = i64s
        .iter()
        .map(|array_elem| array_elem.map(|value| value + 1))
        .collect::<Int64Array>();

    Ok(ColumnarValue::from(Arc::new(new_array) as ArrayRef))
}

Function Registration

pub fn init() {
    let udf = create_udf(
        "add_one",           // Function name
        vec![DataType::Int64], // Parameter type
        DataType::Int64,       // Return type
        Volatility::Immutable, // Function stability
        Arc::new(add_one),     // Function implementation
    );
    processor::udf::scalar_udf::register(udf);
}

Usage

  1. Ensure you have Rust and Cargo installed
  2. Clone the ArkFlow plugin examples repository: 
    git clone https://github.com/arkflow-rs/arkflow-plugin-examples.git
cd arkflow-plugin-examples
  3. Build the project: 
    cargo build

Using in SQL

Once the UDF is registered, you can use it in SQL queries just like built-in functions:

SELECT add_one(column_name) FROM your_table;

Extended Examples

You can create more complex UDFs based on this example:

  • Process multiple input parameters
  • Return different data types
  • Implement more complex business logic