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+```sql
+-- 增删改
+INSERT INTO products (maker, model, type) 
+VALUES ('I', '3008', 'printer');
+INSERT INTO sales (customer_id, model, quantity, day, paid, type_of_payment)
+VALUES ('1112223333', '3008', 2, '2024-01-01', 200, 'cash');
+INSERT INTO customers (customer_id, firstname, lastname, city, address, email)
+VALUES ('1112223333', 'Lisa', 'Smith', 'Dublin', '5 Main St.', 'lisa@example.com');
+
+-- 更新
+UPDATE pcs 
+SET price = 2200 
+WHERE model = '1001';
+
+
+UPDATE sales 
+SET type_of_payment = 'visa credit' 
+WHERE customer_id = '1122334455' AND model = '2010';
+
+UPDATE customers 
+SET email = 'norah.jones@yahoo.com' 
+WHERE customer_id = '9999999999';
+
+-- 删除
+DELETE FROM printers 
+WHERE model = '3006';
+
+
+DELETE FROM sales 
+WHERE day = '2013-12-17';
+
+DELETE FROM customers 
+WHERE customer_id = '1231231231';
+
+
+
+
+-- 完成数据库新用户创建、
+CREATE USER `zds`
+-- 授权访问数据库、
+GRANT  SELECT, UPDATE, INSERT ON TABLE sales TO zds;
+
+-- 授权用户传递权限（with grant option）
+GRANT SELECT ON sdut.sales TO zds WITH GRANT OPTION
+-- 收回用户的sales表更新权限
+REVOKE UPDATE ON sdut.sales FROM zds;
+
+-- 收回所有权限（彻底回收）
+REVOKE ALL PRIVILEGES ON sdut.sales FROM zds
+--  删除创建的用户
+DROP USER zds;
+
+
+
+
+
+-- 触发器
+-- 1
+CREATE TABLE pcprice_log (
+    log_id INT AUTO_INCREMENT PRIMARY KEY,
+    model VARCHAR(10) NOT NULL,
+    old_price DECIMAL(10,2) NOT NULL,
+    new_price DECIMAL(10,2) NOT NULL
+);
+
+
+CREATE TRIGGER insert_pcpricelog_values_when_pc_price_changed
+AFTER UPDATE ON pcs
+FOR EACH ROW
+BEGIN
+  IF OLD.price != NEW.price THEN
+    INSERT INTO pcprice_log (model, old_price, new_price) 
+    VALUES (OLD.model, OLD.price, NEW.price);
+  END IF;
+END;
+
+-- 测试
+-- INSERT INTO pcs (model, price, speed, ram, hd ) 
+-- VALUES ('1005', 200, 3.0, 8, 512);
+-- UPDATE pcs set price=22 WHERE model=1005
+
+
+-- 2定义AFTER行级触发器，当删除顾客表Customer中的一个顾客信息后，同时删除购买信息表Sales中该顾客的所有购买记录
+
+CREATE TRIGGER deleteCustomer
+after DELETE on customers 
+for each row 
+BEGIN
+    DELETE FROM sales 
+    WHERE customer_id = OLD.customer_id;
+END
+
+-- -- 测试
+-- DELETE FROM customers WHERE customer_id=9999999999
+
+-- 3需要对在表上进行DML操作的用户进行安全检查，看是否具有合适的特权
+-- 权限表：存储用户可执行的DML权限（JSON数组格式，如["insert","update"]）
+CREATE TABLE IF NOT EXISTS userPrivilege (
+    id INT PRIMARY KEY AUTO_INCREMENT,
+    user_name VARCHAR(100) NOT NULL UNIQUE COMMENT '用户名（格式：user@host，如root@localhost，匹配CURRENT_USER()）',
+    privilege JSON NOT NULL COMMENT '权限列表，JSON数组，值为"insert"/"update"/"delete"（统一小写）',
+    create_time DATETIME DEFAULT CURRENT_TIMESTAMP COMMENT '权限创建时间'
+);
+
+-- 插入测试数据：给用户zds@localhost分配INSERT/UPDATE权限，不给DELETE权限
+INSERT INTO userPrivilege (user_name, privilege)
+VALUES ('zds@localhost', '["insert", "update"]');
+-- 权限表：存储用户可执行的DML权限（JSON数组格式，如["insert","update"]）
+CREATE TABLE IF NOT EXISTS userPrivilege (
+    id INT PRIMARY KEY AUTO_INCREMENT,
+    user_name VARCHAR(100) NOT NULL UNIQUE COMMENT '用户名（格式：user@host，如root@localhost，匹配CURRENT_USER()）',
+    privilege JSON NOT NULL COMMENT '权限列表，JSON数组，值为"insert"/"update"/"delete"（统一小写）',
+    create_time DATETIME DEFAULT CURRENT_TIMESTAMP COMMENT '权限创建时间'
+);
+
+-- 插入测试数据：给用户zds@localhost分配INSERT/UPDATE权限，不给DELETE权限
+INSERT INTO userPrivilege (user_name, privilege)
+VALUES ('zds@localhost', '["insert", "update"]');
+
+DELIMITER //
+CREATE TRIGGER trg_check_update_priv
+BEFORE UPDATE ON customers -- 同样可替换为目标表
+FOR EACH ROW
+BEGIN
+    DECLARE user_priv JSON;
+    DECLARE has_update INT DEFAULT 0;
+    DECLARE curr_user VARCHAR(100) DEFAULT CURRENT_USER();
+
+    -- 查询当前用户权限
+    SELECT privilege INTO user_priv
+    FROM userPrivilege
+    WHERE user_name = curr_user;
+
+    -- 判断是否有"update"权限
+    IF user_priv IS NOT NULL THEN
+        SET has_update = JSON_CONTAINS(user_priv, '"update"');
+    END IF;
+
+    -- 无权限抛错
+    IF has_update = 0 THEN
+        SIGNAL SQLSTATE '45000'
+        SET MESSAGE_TEXT = CONCAT('安全检查失败：用户 [', curr_user, '] 无 ', TABLE_NAME, ' 表的 UPDATE 权限');
+    END IF;
+END //
+DELIMITER ;
+DELIMITER //
+CREATE TRIGGER trg_check_delete_priv
+BEFORE DELETE ON customers -- 同样可替换为目标表
+FOR EACH ROW
+BEGIN
+    DECLARE user_priv JSON;
+    DECLARE has_delete INT DEFAULT 0;
+    DECLARE curr_user VARCHAR(100) DEFAULT CURRENT_USER();
+
+    -- 查询当前用户权限
+    SELECT privilege INTO user_priv
+    FROM userPrivilege
+    WHERE user_name = curr_user;
+
+    -- 判断是否有"delete"权限
+    IF user_priv IS NOT NULL THEN
+        SET has_delete = JSON_CONTAINS(user_priv, '"delete"');
+    END IF;
+
+    -- 无权限抛错
+    IF has_delete = 0 THEN
+        SIGNAL SQLSTATE '45000'
+        SET MESSAGE_TEXT = CONCAT('安全检查失败：用户 [', curr_user, '] 无 ', TABLE_NAME, ' 表的 DELETE 权限');
+    END IF;
+END //
+DELIMITER ;
+
+-- 4如果某个特定客户ID的购买记录从销售表中删除后，则从客户表中删除该客户。
+CREATE TRIGGER deleteCustomer_by4
+AFTER DELETE on sales
+for each row 
+BEGIN 
+        DELETE FROM customers 
+        WHERE customer_id = OLD.customer_id;
+END
+
+CREATE TRIGGER discount AFTER INSERT ON sales FOR EACH ROW
+BEGIN
+    DECLARE
+      sum_paid DECIMAL ( 12, 2 );
+    DECLARE
+      discount DECIMAL ( 5, 2 );
+    SELECT
+      sum( paid ) INTO sum_paid 
+    FROM
+      sales 
+    WHERE
+      customer_id = NEW.customer_id;
+    SELECT
+      discount INTO discount 
+    FROM
+      customers 
+    WHERE
+      customer_id = NEW.customer_id;
+    IF
+      SUM_paid > 10000 
+      AND discount < 10.00 THEN
+        UPDATE customers 
+        SET discount = 10.00 
+        WHERE
+          customer_id = NEW.customer_id;
+        
+      END IF;
+    
+  END
+  
+  
+--   6在客户中添加一个新的"AllPaid"栏，如果插入或更新或删除一个销售元组，那么修改该客户的"AllPaid"的值
+
+ALTER TABLE customers
+ADD COLUMN AllPaid DECIMAL(12,2) NOT NULL DEFAULT 0.00 
+
+CREATE TRIGGER  insert_value_customer
+AFTER INSERT on customers
+for each ROW
+BEGIN
+ UPDATE customers 
+ set AllPaid =(
+  SELECT SUM(paid) FROM sales
+  WHERE customer_id = NEW.customer_id
+ )
+ WHERE customer_id = NEW.customer_id;
+ END
+ 
+ 
+ CREATE TRIGGER  UPDATE_value_customer
+AFTER UPDATE on customers
+for each ROW
+BEGIN
+ UPDATE customers 
+ set AllPaid =(
+  SELECT SUM(paid) FROM sales
+  WHERE customer_id = NEW.customer_id
+ )
+ WHERE customer_id = NEW.customer_id;
+ END
+ 
+ 
+ CREATE TRIGGER  DELETE_value_customer
+AFTER DELETE on customers
+for each ROW
+BEGIN
+ UPDATE customers 
+ set AllPaid =(
+  SELECT SUM(paid) FROM sales
+  WHERE customer_id = old.customer_id
+ )
+ WHERE customer_id = old.customer_id;
+ END
+-- 测试
+
+
+```
+