PostgreSQL创建触发器的实现示例

CREATE TABLE user_logs (
    log_id SERIAL PRIMARY KEY,
    user_id UUID,
    action TEXT,
    log_time TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

CREATE OR REPLACE FUNCTION log_user_insert() RETURNS TRIGGER AS $$
BEGIN
    INSERT INTO user_logs (user_id, action)
    VALUES (NEW.id, 'User created');
    RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER user_insert_trigger
AFTER INSERT ON users
FOR EACH ROW
EXECUTE FUNCTION log_user_insert();

ALTER TABLE users ADD COLUMN updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP;

CREATE OR REPLACE FUNCTION update_timestamp() RETURNS TRIGGER AS $$
BEGIN
    NEW.updated_at = CURRENT_TIMESTAMP;
    RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER update_users_timestamp
BEFORE UPDATE ON users
FOR EACH ROW
EXECUTE FUNCTION update_timestamp();

CREATE OR REPLACE FUNCTION prevent_delete() RETURNS TRIGGER AS $$
BEGIN
    RAISE EXCEPTION '不允许删除数据!';
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER prevent_users_deletion
BEFORE DELETE ON users
FOR EACH ROW
EXECUTE FUNCTION prevent_delete();

SELECT tgname, relname, tgtype, proname 
FROM pg_trigger 
JOIN pg_class ON pg_trigger.tgrelid = pg_class.oid
JOIN pg_proc ON pg_trigger.tgfoid = pg_proc.oid
WHERE NOT tgisinternal;

DROP TRIGGER IF EXISTS user_insert_trigger ON users;

DROP FUNCTION IF EXISTS log_user_insert();