更新PostgreSQL函数中的行和变量

CREATE TABLE employees (
    id SERIAL PRIMARY KEY,
    name VARCHAR(100),
    salary NUMERIC
);

CREATE OR REPLACE FUNCTION update_employee_salary(employee_id INTEGER, new_salary NUMERIC)
RETURNS VOID AS $$
DECLARE
    old_salary NUMERIC;
BEGIN
    -- 获取旧薪水
    SELECT salary INTO old_salary FROM employees WHERE id = employee_id;

    -- 更新薪水
    UPDATE employees SET salary = new_salary WHERE id = employee_id;

    -- 输出更新前后的薪水差异
    RAISE NOTICE 'Employee % salary updated from %.2f to %.2f', employee_id, old_salary, new_salary;
END;
$$ LANGUAGE plpgsql;

DECLARE
    old_salary NUMERIC;
BEGIN
    -- 确保查询结果赋值给变量
    SELECT salary INTO old_salary FROM employees WHERE id = employee_id;
    ...
END;

BEGIN
    -- 锁定要更新的行
    SELECT salary INTO old_salary FROM employees WHERE id = employee_id FOR UPDATE;

    -- 更新薪水
    UPDATE employees SET salary = new_salary WHERE id = employee_id;
    ...
END;