mysql常用语句练习-基于ecshop2.7.3数据库(1)

SELECT * FROM ecs_goods WHERE goods_id = 1;
SELECT goods_id, goods_name FROM ecs_goods WHERE goods_id = 1;
SELECT goods_id,cat_id,goods_name FROM ecs_goods WHERE cat_id != 3;
SELECT goods_id,cat_id,goods_name FROM ecs_goods WHERE cat_id <> 3;
SELECT goods_id,cat_id,goods_name,shop_price FROM ecs_goods WHERE shop_price > 3000;
SELECT goods_id,cat_id,goods_name,shop_price FROM ecs_goods WHERE shop_price <= 100;

SELECT goods_id,cat_id,goods_name,shop_price FROM ecs_goods WHERE cat_id = 4 OR cat_id = 3;
SELECT goods_id,cat_id,goods_name,shop_price FROM ecs_goods WHERE cat_id IN( 3, 4 );

SELECT goods_id,cat_id,goods_name,shop_price FROM ecs_goods WHERE shop_price BETWEEN 100 AND 858;

SELECT goods_id,cat_id,goods_name,shop_price FROM ecs_goods WHERE cat_id != 3 AND cat_id != 4
SELECT goods_id,cat_id,goods_name,shop_price FROM ecs_goods WHERE cat_id NOT IN( 3, 4 );
SELECT goods_id,cat_id,goods_name,shop_price FROM ecs_goods WHERE cat_id NOT BETWEEN 3 AND 4

SELECT goods_id,cat_id,goods_name,shop_price FROM ecs_goods WHERE ( shop_price > 100 AND shop_price < 300 )
OR ( shop_price > 1000 AND shop_price < 3000 );

SELECT goods_id,cat_id,goods_name,shop_price,click_count FROM ecs_goods WHERE (cat_id = 3 ) AND ( shop_price >= 1000 AND shop_price <= 3000 )
AND ( click_count > 5 )

 

SELECT * FROM ecs_goods WHERE cat_id IN ( 2, 3, 4, 5 )

SELECT goods_id,cat_id,goods_name FROM ecs_goods WHERE goods_name LIKE '诺基亚%'

 

 #把表中字段num取值范围为20~29之间的值变成20【注：ecshop2.7.3没有这个ecs_mian1这个表，可以自己创建一个，他就一个字段num, int类型，然后填充一些测试数据】

UPDATE ecs_mian1 SET num = ( FLOOR( num / 10 ) * 10 ) WHERE num >= 20 AND num <= 29

 #把表中字段num取值范围为30~39之间的值变成30

UPDATE ecs_mian1 SET num = ( FLOOR( num / 10 ) * 10 ) WHERE num BETWEEN 30 AND 39

 

#以”诺基亚"开头的商品

SELECT goods_id, goods_name FROM ecs_goods WHERE goods_name LIKE '诺基亚%';

#截取"诺基亚"后面的商品名称，并用"小米"开始 连接起来
SELECT goods_id, CONCAT( '小米', SUBSTRING( goods_name, 4 ) ) FROM ecs_goods WHERE goods_name LIKE '诺基亚%';

#截取"诺基亚"后面的商品名称，并用"小米"开始 连接起来后更新
UPDATE ecs_goods SET goods_name = CONCAT( '小米', SUBSTRING( goods_name, 4 ) ) WHERE goods_name LIKE '诺基亚%'

#以上面的语句相反
UPDATE ecs_goods SET goods_name = CONCAT( '诺基亚', SUBSTRING( goods_name, 4 ) ) WHERE goods_name LIKE '小米%'

 

关于NULL:

SELECT NULL = NULL
SELECT NULL != NULL

#建表
CREATE TABLE ghost_user_info(
id INT( 3 ),
user_name VARCHAR( 20 )
)CHARSET utf8 ENGINE MYISAM;

#插入测试数据
INSERT INTO ghost_user_info VALUES( 1, '张三' );
INSERT INTO ghost_user_info VALUES( 2, NULL );

#user_name不等于NULL的记录，不能这样写
SELECT * FROM ghost_user_info WHERE user_name != NULL

#user_name不等于NULL的记录，应该这样写
SELECT * FROM ghost_user_info WHERE user_name IS NOT NULL

#同样的，等于NULL的记录应该是 IS NULL而不是 = NULL
SELECT * FROM ghost_user_info WHERE user_name = NULL
SELECT * FROM ghost_user_info WHERE user_name IS NULL

 #统计函数

SELECT AVG( shop_price ) FROM ecs_goods;
SELECT MAX( shop_price ) FROM ecs_goods;
SELECT MIN( shop_price ) FROM ecs_goods;
SELECT COUNT(*) FROM ecs_goods;
SELECT SUM( shop_price ) / COUNT(*) FROM ecs_goods;

#积压货款
SELECT SUM( shop_price * goods_number ) FROM ecs_goods;

 #统计每个分类的商品平均价格, group比较耗费资源（先按cat_id排序，再统计）

SELECT cat_id,AVG( shop_price ) FROM ecs_goods GROUP BY cat_id;

#查询每个分类下，商品的数量
SELECT cat_id, COUNT(*) FROM ecs_goods GROUP BY cat_id;

#每个分类下最贵的产品
SELECT cat_id, MAX(shop_price) FROM ecs_goods GROUP BY cat_id;

 

#本店价格比市场价格小200以上的商品
SELECT goods_id, goods_name, market_price - shop_price FROM ecs_goods WHERE market_price - shop_price > 200

#下面的语句，报错（Unknown column 'discount_price' in 'where clause' ）,discount_price这个别名是结果集中(存在内存中）的，where后面的字段需要是磁盘表中的字段

SELECT goods_id, goods_name, ( market_price - shop_price ) AS discount_price FROM ecs_goods WHERE discount_price > 200

#可以用having关键字过滤查询出来的结果集
SELECT goods_id, goods_name, ( market_price - shop_price ) AS discount_price FROM ecs_goods WHERE 1 HAVING discount_price > 200

#多列排序

SELECT goods_id, cat_id, goods_name, shop_price FROM ecs_goods ORDER BY cat_id ASC, shop_price DESC;

 

#查询最新的商品1
SELECT goods_id, goods_name, cat_id FROM ecs_goods ORDER BY goods_id DESC LIMIT 0,1
#下面两句组合，等于后面的where子查询
SELECT goods_Id, goods_name,cat_id FROM ecs_goods WHERE goods_id = 32
SELECT MAX( goods_id ) FROM ecs_goods;
#(where子查询)查询最新的商品2
SELECT goods_Id, goods_name,cat_id FROM ecs_goods WHERE goods_id = ( SELECT MAX( goods_id ) FROM ecs_goods );

 

#from子查询：每一个分类下，最大的产品id( 最新的产品 )
SELECT goods_id, goods_name, cat_id FROM ecs_goods ORDER BY cat_id ASC, goods_id DESC
#把上面的语句 当前一个临时的表，放在from后面 组成一个from子查询
SELECT goods_id, goods_name, cat_id FROM ( SELECT goods_id, goods_name, cat_id FROM ecs_goods ORDER BY cat_id ASC, goods_id DESC ) AS tmp GROUP BY cat_id

 

#查询有商品的分类

SELECT * FROM ecs_category c WHERE EXISTS( SELECT * FROM ecs_goods g WHERE g.cat_id = c.cat_id );

 #查询没有商品的分类

SELECT * FROM ecs_category c WHERE not EXISTS( SELECT * FROM ecs_goods g WHERE g.cat_id = c.cat_id );

 

参考：

MySQL EXISTS 和 NOT EXISTS 子查询语法如下：

• SELECT … FROM table WHERE EXISTS (subquery)

该语法可以理解为：将主查询的数据，放到子查询中做条件验证，根据验证结果（TRUE 或 FALSE）来决定主查询的数据结果是否得以保留。