ALTER FUNCTION

ユーザー定義関数を変更します。サポートされる関数タイプは、Scalar SQL、Tabular SQL、Embedded 関数です。

構文

Scalar SQL 関数の場合

ALTER FUNCTION [ IF EXISTS ] <function_name>
    ( [<parameter_list>] )
    RETURNS <return_type>
    AS $$ <expression> $$
    [ DESC='<description>' ]

Tabular SQL 関数の場合

ALTER FUNCTION [ IF EXISTS ] <function_name>
    ( [<parameter_list>] )
    RETURNS TABLE ( <column_definition_list> )
    AS $$ <sql_statement> $$
    [ DESC='<description>' ]

Embedded 関数の場合

ALTER FUNCTION [ IF EXISTS ] <function_name>
    ( [<parameter_list>] )
    RETURNS <return_type>
    LANGUAGE <language>
    [IMPORTS = ('<import_path>', ...)]
    [PACKAGES = ('<package_path>', ...)]
    HANDLER = '<handler_name>'
    AS $$ <function_code> $$
    [ DESC='<description>' ]

例

Scalar SQL 関数の変更

-- Create a scalar function
CREATE FUNCTION calculate_tax(income DECIMAL)
RETURNS DECIMAL
AS $$ income * 0.2 $$;

-- Modify the function to use progressive tax rate
ALTER FUNCTION calculate_tax(income DECIMAL)
RETURNS DECIMAL
AS $$
  CASE
    WHEN income <= 50000 THEN income * 0.15
    ELSE income * 0.25
  END
$$;

Tabular SQL 関数の変更

-- Create a table function
CREATE FUNCTION get_employees()
RETURNS TABLE (id INT, name VARCHAR(100))
AS $$ SELECT id, name FROM employees $$;

-- Modify to include department and salary
ALTER FUNCTION get_employees()
RETURNS TABLE (id INT, name VARCHAR(100), department VARCHAR(100), salary DECIMAL)
AS $$ SELECT id, name, department, salary FROM employees $$;

Embedded 関数の変更

-- Create a Python function
CREATE FUNCTION simple_calc(x INT)
RETURNS INT
LANGUAGE python
HANDLER = 'calc'
AS $$
def calc(x):
    return x * 2
$$;

-- Modify to use a different calculation
ALTER FUNCTION simple_calc(x INT)
RETURNS INT
LANGUAGE python
HANDLER = 'calc'
AS $$
def calc(x):
    return x * 3 + 1
$$;