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Extension descriptor (YAML)

Dynamic function invocation - call any scalar function or macro by name at runtime

Compatibility Matrix

This table covers all DuckDB releases that have not reached end-of-life, including LTS releases, and shows the 2 most recent patch releases of each. Older patch releases are not listed, but the extension may be available for them as well.

Installing and Loading

INSTALL func_apply FROM community;
LOAD func_apply;

Example

-- Load the extension
LOAD func_apply;

-- Call scalar functions dynamically
SELECT apply('upper', 'hello world');
-- Result: HELLO WORLD

SELECT apply('substr', 'hello world', 7, 5);
-- Result: world

-- Call table functions dynamically
SELECT * FROM apply_table('range', 5);
-- Returns: 0, 1, 2, 3, 4

SELECT * FROM apply_table('generate_series', 1, 10, 2);
-- Returns: 1, 3, 5, 7, 9

-- Check if a function exists before calling
SELECT function_exists('my_custom_func');
-- Result: true/false

About func_apply

The FuncApply extension enables dynamic function invocation in DuckDB, allowing you to call any scalar function or macro by name at runtime. This is useful for data-driven transformations, dynamic SQL generation, and building flexible data pipelines.

Functions

Use Cases

Data-Driven Transformations

-- Store transformation rules in a table
CREATE TABLE transforms (column_name VARCHAR, func_name VARCHAR);
INSERT INTO transforms VALUES ('name', 'upper'), ('email', 'lower');

-- Apply transformations dynamically
SELECT apply(t.func_name, d.value) as result
FROM data d JOIN transforms t ON d.column = t.column_name;

Routing With func_dispatch

CREATE MACRO clean_git(p)   AS regexp_replace(p, '^git://', '');
CREATE MACRO clean_http(p)  AS regexp_replace(p, '^https?://', '');
CREATE MACRO clean_other(p) AS p;

SELECT func_dispatch(MAP{'git':   'clean_git',
                         'https': 'clean_http',
                         '*':     'clean_other'},
                     split_part(url, ':', 1),
                     url) AS cleaned
FROM urls;

The '*' entry catches any key the map does not name. Unlike apply() with a function name that is not a constant, func_dispatch binds every candidate in a constant routing map at plan time, so the result keeps its real type instead of collapsing to VARCHAR:

CREATE MACRO pair(x) AS [x, x];
SELECT typeof(func_dispatch(MAP{'a': 'pair'}, 'a', 7));  -- INTEGER[]

All routes in a constant map must accept the forwarded arguments, and the session security policy applies to every route including '*'.

Dynamic Function Selection

-- Choose function based on data type
SELECT apply(
    CASE typeof(value)
        WHEN 'VARCHAR' THEN 'upper'
        WHEN 'INTEGER' THEN 'abs'
    END,
    value
) FROM my_table;

Supported Function Types

• Scalar functions (e.g., upper, abs, substr)
• Macros (e.g., list_sum, list_reverse)

Aggregate and table functions are not supported.

Security Model

apply and apply_table run on the caller's own context — they add no privilege beyond the SQL the caller could already execute directly. They are a dynamic-dispatch convenience, not a sandbox.

For scenarios that embed func_apply and want to restrict which functions can be invoked (e.g. accepting a function name from less-trusted input), an optional, opt-in policy is available. It is per session and defaults to none (no restriction):

The policy lives on the session's ClientContext and does not leak across connections. Versions before 0.2.0 stored it process-globally and could quote-escape injected identifiers — see security advisory GHSA-55g5-vp25-phpg; upgrade to 0.2.0 (DuckDB v1.5.4 track).

Added Functions

Overloaded Functions

This extension does not add any function overloads.

Added Types

This extension does not add any types.

Added Settings

This extension does not add any settings.