触发器的类型

触发器可以指定为触发：

• BEFORE 在一行上尝试操作 - 插入，更新或删除;
• AFTER 操作已完成 - 插入，更新或删除;
• INSTEAD OF 在视图上插入，更新或删除的操作。

标记为的触发器：

• FOR EACH ROW 为操作修改的每一行调用一次;
• 对于任何给定的操作，FOR EACH STATEMENT 都被称为 onde。

准备执行示例

CREATE TABLE company (
    id          SERIAL PRIMARY KEY NOT NULL,
    name        TEXT NOT NULL,
    created_at  TIMESTAMP,
    modified_at TIMESTAMP DEFAULT NOW()
)

CREATE TABLE log (
    id          SERIAL PRIMARY KEY NOT NULL,
    table_name  TEXT NOT NULL,
    table_id    TEXT NOT NULL,
    description TEXT NOT NULL,
    created_at  TIMESTAMP DEFAULT NOW()
)

单插入触发器

第 1 步：创建你的功能

CREATE OR REPLACE FUNCTION add_created_at_function()
  RETURNS trigger AS $BODY$
BEGIN
  NEW.created_at := NOW();
  RETURN NEW;
END $BODY$
LANGUAGE plpgsql;

第 2 步：创建触发器

CREATE TRIGGER add_created_at_trigger
BEFORE INSERT
ON company
FOR EACH ROW
EXECUTE PROCEDURE add_created_at_function();

第 3 步：测试它

INSERT INTO company (name) VALUES ('My company');
SELECT * FROM company;

触发多种用途

第 1 步：创建你的功能

CREATE OR REPLACE FUNCTION add_log_function()
  RETURNS trigger AS $BODY$
DECLARE
  vDescription TEXT;
  vId INT;
  vReturn RECORD;
BEGIN
    vDescription := TG_TABLE_NAME || ' ';
     IF (TG_OP = 'INSERT') THEN
        vId := NEW.id;
        vDescription := vDescription || 'added. Id: ' || vId;
        vReturn := NEW;
    ELSIF (TG_OP = 'UPDATE') THEN
        vId := NEW.id;
        vDescription := vDescription || 'updated. Id: ' || vId;
        vReturn := NEW;
    ELSIF (TG_OP = 'DELETE') THEN
        vId := OLD.id;
        vDescription := vDescription || 'deleted. Id: ' || vId;
        vReturn := OLD;
    END IF;

    RAISE NOTICE 'TRIGER called on % - Log: %', TG_TABLE_NAME, vDescription;

    INSERT INTO log 
        (table_name, table_id, description, created_at) 
        VALUES
        (TG_TABLE_NAME, vId, vDescription, NOW());

    RETURN vReturn;
END $BODY$
  LANGUAGE plpgsql;

第 2 步：创建触发器

CREATE TRIGGER add_log_trigger
AFTER INSERT OR UPDATE OR DELETE
ON company
FOR EACH ROW
EXECUTE PROCEDURE add_log_function();

第 3 步：测试它

INSERT INTO company (name) VALUES ('Company 1');
INSERT INTO company (name) VALUES ('Company 2');
INSERT INTO company (name) VALUES ('Company 3');
UPDATE company SET name='Company new 2' WHERE name='Company 2';
DELETE FROM company WHERE name='Company 1';
SELECT * FROM log;