Function parse_expr_field

datafusion/functions-window/src/lead_lag.rs:372–387

Returns the field of the default value(if provided) when the expression is `NULL`. Otherwise, returns the expression field unchanged.

(input_fields: &[FieldRef])

///
/// Otherwise, returns the expression field unchanged.
fn parse_expr_field(input_fields: &[FieldRef]) -> Result<FieldRef> {
    assert!(!input_fields.is_empty());
    let expr_field = input_fields.first().unwrap_or(&NULL_FIELD);

    // Handles the most common case where NULL is unexpected
    if !expr_field.data_type().is_null() {
        return Ok(expr_field.as_ref().clone().with_nullable(true).into());
    }

    let default_value_field = input_fields.get(2).unwrap_or(&NULL_FIELD);
    Ok(default_value_field
        .as_ref()
        .clone()
        .with_nullable(true)
        .into())
}

/// Handles type coercion and null value refinement for default value
/// argument depending on the data type of the input expression.