在 PostgreSQL 數據庫中，可以通過以下步驟實現可更新視圖：

1. 創建一個視圖并確保其滿足以下條件：

   • 視圖必須包含唯一的行標識符，即必須包含一個或多個可以唯一標識每一行的列。
   • 視圖必須包含從具有 INSERT、UPDATE 和 DELETE 權限的角色能夠訪問的列。

2. 創建 INSTEAD OF 觸發器來處理對視圖的 INSERT、UPDATE 和 DELETE 操作。這些觸發器將捕獲對視圖的操作，并將其轉換為對基礎表的操作。

下面是一個示例，演示了如何創建一個可更新的視圖和相應的觸發器：

-- 創建一個基礎表
CREATE TABLE employees (
    id SERIAL PRIMARY KEY,
    name VARCHAR(50),
    department VARCHAR(50)
);

-- 向基礎表中插入一些數據
INSERT INTO employees (name, department) VALUES ('Alice', 'HR');
INSERT INTO employees (name, department) VALUES ('Bob', 'IT');

-- 創建一個視圖
CREATE VIEW employee_view AS
SELECT id, name, department
FROM employees;

-- 創建一個 INSTEAD OF 觸發器處理對視圖的 INSERT 操作
CREATE OR REPLACE FUNCTION insert_employee()
RETURNS TRIGGER AS $$
BEGIN
    INSERT INTO employees (name, department)
    VALUES (NEW.name, NEW.department);
    RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER insert_employee_trigger
INSTEAD OF INSERT ON employee_view
FOR EACH ROW
EXECUTE FUNCTION insert_employee();

-- 創建一個 INSTEAD OF 觸發器處理對視圖的 UPDATE 操作
CREATE OR REPLACE FUNCTION update_employee()
RETURNS TRIGGER AS $$
BEGIN
    UPDATE employees
    SET name = NEW.name, department = NEW.department
    WHERE id = NEW.id;
    RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER update_employee_trigger
INSTEAD OF UPDATE ON employee_view
FOR EACH ROW
EXECUTE FUNCTION update_employee();

-- 創建一個 INSTEAD OF 觸發器處理對視圖的 DELETE 操作
CREATE OR REPLACE FUNCTION delete_employee()
RETURNS TRIGGER AS $$
BEGIN
    DELETE FROM employees
    WHERE id = OLD.id;
    RETURN OLD;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER delete_employee_trigger
INSTEAD OF DELETE ON employee_view
FOR EACH ROW
EXECUTE FUNCTION delete_employee();

-- 現在可以對 employee_view 視圖進行 INSERT、UPDATE 和 DELETE 操作
INSERT INTO employee_view (name, department) VALUES ('Charlie', 'Finance');
UPDATE employee_view SET department = 'Marketing' WHERE id = 1;
DELETE FROM employee_view WHERE id = 2;

通過以上步驟，您可以在 PostgreSQL 數據庫中實現可更新的視圖。