MySQL学习（一）

/*
单个表列，多个表列，全部表列
*/

--  检索单个列
SELECT prod_name FROM Products;  

SELECT prod_name
FROM Products;

SELECT prod_id,prod_name,prod_price
FROM Products;

SELECT * from Products;

SELECT vend_id FROM Products;


-- 使用 DISTINCT 只返回不一样（具备惟一性）的值
-- DISTINCT 做用于全部的列 
SELECT DISTINCT vend_id  
FROM Products;                     

-- 表示从第5行开始返回3个数据
SELECT prod_name
FROM Products
LIMIT 3 OFFSET 5;  

-- 简写方式，从第3行开始返回5个数据
SELECT prod_name
FROM Products
LIMIT 3,5;  


/*
排序检索数据
*/


-- 注意 ORDER BY 必须放置查询语句最后，否则会出现错误
SELECT prod_name
FROM Products
ORDER BY prod_name;  


-- 按多个列排序
SELECT prod_id,prod_price,prod_name
FROM Products
ORDER BY prod_price,prod_name;


-- 按列位置排序，不用指定列名
SELECT prod_id,prod_price,prod_name
FROM Products
ORDER BY 2, 3;


-- 降序排序
SELECT prod_id,prod_price,prod_name
FROM Products
ORDER BY prod_price DESC;


-- 警告：DESC 只做用于当前列名，若是须要对多个列进行降序排序，必须对每一列指定 DESC 关键字
SELECT prod_id,prod_price,prod_name
FROM Products
ORDER BY prod_price DESC, prod_name DESC;