INSTALL func_apply FROM community;
LOAD func_apply;

-- 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

-- 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;

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