《SQL必知必会》—— 视图

视图

-- 利用视图简化复杂的联结
CREATE VIEW productscustomers AS
SELECT cust_name, cust_contact, prod_id
FROM customers, orders, orderitems
WHERE orders.cust_id = customers.cust_id AND orders.order_num = orderitems.order_num;   -- 返回订购任意产品的所有顾客

SELECT * FROM productscustomers WHERE prod_id = 'RGAN01';                               -- 返回订购了RGAN01的所有顾客

-- 利用视图重新格式化检索出的数据
CREATE VIEW VendorLocation AS
SELECT CONCAT(vend_name,' (', vend_country, ')') AS vend_title
FROM vendors;

SELECT * FROM vendorlocation;

-- 使用视图过滤不要的数据
CREATE VIEW CustEmailList AS
SELECT cust_id, cust_name, cust_email
FROM customers WHERE cust_email IS NOT NULL;

SELECT * FROM CustEmailList;

-- 使用视图与计算字段
CREATE VIEW OrderItemsExpanded AS
SELECT order_num, prod_id, quantity, item_price, quantity*item_price AS expanded_price
FROM orderitems;

SELECT * FROM OrderItemsExpanded WHERE order_num = 20008;