NULL Handling

By default, DuckDB automatically propagates NULLs: if any argument to a function is NULL, the result is NULL without your function callback being called. This matches the SQL standard and works well for most functions.

However, some functions need to handle NULLs explicitly. For example:

• COALESCE — returns the first non-NULL argument
• IS_NULL / IS_NOT_NULL — tests whether the value is NULL
• Custom aggregates that need to count NULLs

NullHandling enum

#![allow(unused)]
fn main() {
use quack_rs::types::NullHandling;

// Default: DuckDB auto-returns NULL for any NULL input
NullHandling::DefaultNullHandling

// Special: DuckDB passes NULLs to your callback
NullHandling::SpecialNullHandling
}

Scalar functions

#![allow(unused)]
fn main() {
use quack_rs::scalar::ScalarFunctionBuilder;
use quack_rs::types::{TypeId, NullHandling};

ScalarFunctionBuilder::new("my_coalesce")
    .param(TypeId::BigInt)
    .param(TypeId::BigInt)
    .returns(TypeId::BigInt)
    .null_handling(NullHandling::SpecialNullHandling)
    .function(my_coalesce_fn)
    .register(con)?;
}

With SpecialNullHandling, your callback must check VectorReader::is_valid(row) for each input column and handle NULLs yourself.

Aggregate functions

#![allow(unused)]
fn main() {
use quack_rs::aggregate::AggregateFunctionBuilder;
use quack_rs::types::{TypeId, NullHandling};

AggregateFunctionBuilder::new("count_with_nulls")
    .param(TypeId::BigInt)
    .returns(TypeId::BigInt)
    .null_handling(NullHandling::SpecialNullHandling)
    .state_size(my_state_size)
    .init(my_init)
    .update(my_update)   // will be called even for NULL rows
    .combine(my_combine)
    .finalize(my_finalize)
    .register(con)?;
}

When to use special NULL handling

If you don't call .null_handling(), the default (DefaultNullHandling) is used automatically.