SQL基础语句

数据库创建

CREATE DATABASE shop;

建表语句

CREATE TABLE Product
(product_id      CHAR(4)      NOT NULL,
 product_name    VARCHAR(100) NOT NULL,
 product_type    VARCHAR(32)  NOT NULL,
 sale_price      INTEGER ,
 purchase_price  INTEGER ,
 regist_date     DATE ,
 PRIMARY KEY (product_id));

添加字段

 ALTER TABLE Product ADD COLUMN product_name_pinyin VARCHAR(100);

字段删除

 ALTER TABLE Product DROP COLUMN test_name;

插入数据

START TRANSACTION;
INSERT INTO Product VALUES ('0001', 'T恤','衣服', 1000, 500, '2009-09-20');
INSERT INTO Product VALUES ('0002', '打孔器', '办公用品', 500, 320, '2009-09-11');
INSERT INTO Product VALUES ('0003', '运动T恤', '衣服', 4000, 2800, NULL);
INSERT INTO Product VALUES ('0004', '菜刀', '厨房用具', 3000, 2800, '2009-09-20');
INSERT INTO Product VALUES ('0005', '高压锅', '厨房用具', 6800, 5000, '2009-01-15');
INSERT INTO Product VALUES ('0006', '叉子', '厨房用具', 500, NULL, '2009-09-20');
INSERT INTO Product VALUES ('0007', '擦菜板', '厨房用具', 880, 790, '2008-04-28');
INSERT INTO Product VALUES ('0008', '圆珠笔', '办公用品', 100, NULL, '2009-11-11');
COMMIT;

更改表名字

RENAME TABLE Poduct TO Product;

给字段设置别名

SELECT product_id as '商品编号',
			 product_name as '商品名称'
 from product

常数查询(自定义常数字段)

SELECT '商品' AS string, --字段名为string,内容为‘商品’
			 38 AS number, 
   '2009-02-24' AS date,
       product_id, product_name
FROM Product;

从结构中删除数据，使用DISTINCT删除某字段中的重复数据

select DISTINCT product_type from Product;

-- 此时null也会被视为某类数据
select distinct purchase_price from product;

算数运算符，注：使用四则运算符(+,-,*,/),null使用运算还是为null

SELECT product_name, sale_price,
		 sale_price * 2 AS 'sale_price_x2'
FROM Product;

使用select进行计算，不需要from

select (100+200)*3 as cal

比较运算符

-- 筛选价格不等于500的数据：
-- null不能使用比较运算符
SELECT product_name, product_type, sale_price
  FROM Product
WHERE sale_price <> 500;

比较运算符和算数运算符的配合使用：

SELECT product_name, sale_price, purchase_price
FROM Product
WHERE sale_price - purchase_price >= 500;

逻辑运算符(not,and和or运算符)

SELECT product_name, product_type, sale_price
  FROM Product
WHERE NOT sale_price >= 1000;

通过括号强化处理：通过括号让OR运算符优先于OR运算符执行

SELECT product_name, product_type, regist_date
	FROM Product
 WHERE product_type = '办公用品'
	 AND (regist_date = '2009-09-11' OR regist_date = '2009-09-20');