MySQL联结表

创建联结

SELECT vend_name, prod_name, prod_price FROM vendors, products WHERE vendors.vend_id = products.vend_id;

WHERE子句的重要性

-- WHERE子句的重要性
-- 笛卡儿积（检索出的行的数目是第一个表的行数乘以第二个表中的行数）
SELECT * FROM vendors;
SELECT * FROM products;
SELECT vend_name, prod_name, prod_price FROM vendors, products;

内联结

SELECT * FROM vendors INNER JOIN products ON vendors.vend_id = products.vend_id;

联结多个表

SELECT * FROM orderitems, products, vendors WHERE products.vend_id = vendors.vend_id AND orderitems.prod_id = products.prod_id AND order_num = 20007;