自学第四章 检索数据
1、检索单个列
SELECT prod_name FROM products;
2、检索多个列
SELECT prod_id, prod_name, prod_price FROM products;
3、检索所有列
SELECT * FROM products;
4、检索不同的行
SELECT vend_id FROM products;
只返回不同值（去重输出）
SELECT DISTINCT vend_id FROM products;
5、限制结果
SELECT prod_name FROM products LIMIT 5;
设置输出范围
SELECT prod_name FROM products LIMIT 5,5;