mysql_高级语法
本篇是在自学Mysql数据库的过程中，观看一个视频时的个人笔记，感觉这个视频还是不错的，对于已经掌握了基本语法，希望通过实际案例来锻炼的同学有很大的帮助。
在文末会附有视频链接，有兴趣的同学可以看一下。
文章目录
-
- 1. 内连接应用
- 2. 外连接查询
- 3. 子查询
-
- 3.1 不同关键字后面的子查询
- 3.2 关联子查询和非关联子查询的区分
- 3.3 分组统计
- 4.DML
-
- 4.1 insert
- 4.2 update
- 4.3 delete
1. 内连接应用
- 列出客户信息和订单日期，并按订单日期排序
SELECT
u.user_id,
u.user_name,
u.eamil,
oi_order_sn,
from_unixtime( oi.add_time ) AS ordertime
FROM
ecs_order_info AS oi
INNER JOIN ecs_users AS u ON oi.user_id = u.user_id
ORDER BY
ordertime;
数据表的“addtime”字段一般是int型，用于存放时间戳，当想要直观的查看某条记录的addtime,我们需要用from_unixtime()将时间戳转换为日期格式，UNIX_TIMESTAMP()即将日期类型 的转换为时间戳显示。
select UNIX_TIMESTAMP('2018-08-08')------------------->1533657600
select from_unixtime(1533657600)--------------------------->2018-08-08 00:00:00
- 列出被购买过的商品的名称，类型名称和交易价格(三表内连接)注意表连接时用那个字段
SELECT
og.goods_id,
og.goods_name,
gt.cat_name,
og.goods_price
FROM
esc_order_goods og INNER JOIN ecs_goods g ON og.goods_id = g.goods_id
INNER JOIN ecs_goods_type gt ON g.goods_type = gt.cat_id;
如果是在表连接时，有对表进行where筛选的话，需要先进行限制在连接，可以提高运行效率
-
显示各订单下每个商品以及该商品的销售额，按照订单号排序
-
列出被购买过的商品的名称，品牌名称和客户信息(
SELECT
og.goods_names,
b.brand_name,
u.user_name
FROM
(
(
( ecs_order_goods og INNER JOIN ecs_goods g ON og.goods_id = g.goods_id )
INNER JOIN ecs_brand b ON g.brand_id = b.brand_id
)
INNER JOIN ecs_order_info oi ON og.order_id = oi.order_id
)
INNER JOIN ecs_users_u ON oi.user_id = USER.id;
可以修改为
SELECT
og.goods_names,
b.brand_name,
u.user_name
FROM
ecs_order_goods og
INNER JOIN ecs_goods g om og.goods_id = g.goods_id
INNER JOIN ecsecs_brand b ON g.brand_id = b.brand_id
INNER JOIN ecs_order_info oi ON og.order_id = oi.order_id
INNER JOIN ecs_users_u ON oi.user_id = USER.id;
- 找出ecshop用户所有的订单信息
SELECT
u.user_name,
oi.order_id,
og.goods_number,
og.goods_price
FROM
( ecs_order_info oi INNER JOIN ecs_users u ON ou.user_id = u.user_id AND u.user_name = 'ecshop' )
INNER JOIN ecs_order ON oi.ORDER = og.order_id;
注意表连接时的and，这里是先选取u表里user_name 为ecshop的行，然后和oi表进行内连接。要注意与where的区别
2. 外连接查询
在这里，刚学的时候会发生不知道用左右连接的情况，其实不用区分，两者是可以装换的，
看你想显示那个表的全部数据，左连接 显示左表全部数据，右连接显示右表全部数据；
想要保留左边表的全部数据，用左连接，先要保留右边表的全部数据，用右连接
- 哪些商品没有被用户购买过
商品表和订单表连接，显示商品表里的全部数据，商品表为主表，没有订单的商品og.goos_id 显示为 NULL，进而可以筛选出
- 商品类型表中哪些商品类型没有出现在商品表中
SELECT
*
FROM
ecs_goods g
LEFT JOIN ecs_order_goods og ON g.goods_id = og.goods_id
WHERE
og.goods_id IS NULL;
要显示商品类型表里的全部数据，且商品类型表在右边，所以用右连接，没有出现在商品表中的商品类型g.goods_type为NULL
- 找出没有购买过诺基亚E66上商品的客户信息表
SELECT
u.*
FROM
( ecs_order_info oi INNER JOIN ecs_order_goods og ON oi.order_id = og.order_id )
RIGHT JOIN ecs_users u ON oi.user_id = u.user_id
WHERE
oi.user_id IS NULL;
可修改为
SELECT
u.*
FROM
ecs_order_info oi
INNER JOIN ecs_order_goods og ON oi.order_id = og.order_id
RIGHT JOIN ecs_users u ON oi.user_id = u.user_id
WHERE
oi.user_id IS NULL;
- 列出从来没有购买过手机的客户名单
SELECT
u.*
FROM
(
(
( ecs_goods g INNER JOIN ecs_goods_type gt ON g.goods_type = gt.cat_id AND gt.cat_name IN ( '手机', '精品手机' ) )
INNER JOIN ecs_order_goods og ON g.goods_id = og.goods_id
)
INNER JOIN ecs_order_info oi ON og.order_id = oi.ORDER
)
RIGHT JOIN ecs_users u ON oi.USER = u.user_id
可修改为
SELECT
u.*
FROM
ecs_goods g
INNER JOIN ecs_goods_type gt ON g.goods_type = gt.cat_id
AND gt.cat_name IN ( "手机"，"精品手机" )
INNER JOIN ecs_order_goods og ON g.goods_id = og.goods_id
INNER JOIN ecs_order_info oi ON og.order_id = oi.ORDER
RIGHT JOIN ecs_users u ON oi.USER = u.user_id
-
所有邮寄方式中那种邮寄方式没有被采用过
-
列出所有商品和各商品有关的所有订单的日期
SELECT
g.goods_id,
g.goods_name,
oi.order_id,
from_unixtime( oi.add_time ) ordertime
FROM
( ecs_order_info oi INNER JOIN ecs_order_goods og ON oi.order_id = og.ORDER )
RIGHT JOIN ecs_goods g ON og.goods_id = g.goods_id;
可修改为
SELECT
g.goods_id,
g.goods_name,
oi.order_id,
from_unixtime( oi.add_time ) ordertime
FROM
ecs_order_info oi
INNER JOIN ecs_order_goods og ON ou.order_id = og.
ORDER RIGHT JOIN ecs_goods g ON og,
goods_id = g.goods_id;
3. 子查询
3.1 不同关键字后面的子查询
- select后面的子查询（列出商品表中各商品的类型名称）
SELECT
goods_id,
goods_name,
( SELECT cat_name FROM ecs_goods_type WHERE cat_id = g.goods_type ) AS type_name
FROM
ecs_goods g;
类型名在 ecs_goods_type中,从里面选出商品对应的类型名称取名为type_nameel
这里还牵涉到mysql执行顺序的问题
- 模拟orcale中的rownum(行编号)
select
(
select count(*)
from ecs_goods g
where g.goods_id <= eg.goods_id
)
goods_id,goods_name,market_price
from ecs_goods eg
order by 1;
- from后面的子查询（哪些用户购买了市场价格大于2000的商品)
SELECT
u.user_id,
u.user_name,
t.market_price
FROM
( ecs_users u INNER JOIN ecs_order_into oi ON u.user_id = oi.user_id )
INNER JOIN ( SELECT * FROM ecs_order_goods og WHERE og.markeyt_rice > 2000 ) AS t ON oi.order_id = t.order_id;
一定不要忘了给虚拟表取别名
- where后面的子查询（找出市场价格与P806相同的商品信息）
SELECT
*
FROM
ecs_goods
WHERE
market_price in ( SELECT markrt_price FROM ecs_goods WHERE goods_name = 'P806' );#P806只有一行信息
SELECT
*
FROM
ecs_goods
WHERE
market_price in ( SELECT markrt_price FROM ecs_goods WHERE brand = 1 LIMIT 0, 1 );#当返回的不止一行是，为防止报错，可以用limit来限制来只取一行
SELECT
*
FROM
ecs_goods
WHERE
goods_id IN ( SELECT gooes_id FROM ecs_order_goods );#哪些商品被购买过
SELECT
*
FROM
ecs_goods
WHERE
goods_id NOT IN ( SELECT gooes_id FROM ecs_order_goods );#哪些商品没被购买过
(in与not in需慎用)
当in或not in 后的表含有空值时，会没有结果，为防止这种情况，可进行限制
SELECT
*
FROM
ecs_brand
WHERE
brand_id NOT IN ( SELECT brand_id FROM ecs_goods WHERE brand_is IS NOT NULL );
3.2 关联子查询和非关联子查询的区分
- 列出购买诺基亚手机的客户信息
SELECT
*
FROM
ecs_users u
WHERE
u.user_id IN (
SELECT
oi.user_id
FROM
(
(
ecs_goods g
INNER JOIN ecs_goods_type gt ON g.goods_type = gt.cat_id
AND gt.cat_name IN ( '手机', '精品手机' )
AND g.goods_name LIKE '诺基亚%'
)
INNER JOIN ecs_order_goods og ON g.goods_id = og.goods_id
)
INNER JOIN ecs_order_info oi ON og.order_id = oi.order_id
);
- 找出购买了诺基亚手机但没有购买摩托罗拉手机的客户信息
SELECT
*
FROM
ecs_users u
WHERE
u.user_id IN (
SELECT
oi.user_id
FROM
(
(
ecs_goods g
INNER JOIN ecs_goods_type gt ON g.goods_type = gt.cat_id
AND gt.cat_name IN ( '手机', '精品手机' )
AND g.goods_name LIKE '诺基亚%'
)
INNER JOIN ecs_order_goods og ON g.goods_id = og.goods_id
)
INNER JOIN ecs_order_info oi ON og.order_id = oi.order_id
)
AND u.uer_id NOT IN (
SELECT
oi.user_id
FROM
(
(
ecs_goods g
INNER JOIN ecs_goods_type gt ON g.goods_type = gt.cat_id
AND gt.cat_name IN ( '手机', '精品手机' )
AND g.goods_name LIKE '摩托罗拉'
)
INNER JOIN ecs_order_goods og ON g.goods_id = og.goods_id
)
INNER JOIN ecs_order_info oi ON og.order_id = oi.order_id
);
- 哪些商品从未被人购买过
3.3 分组统计
- 统计每种类型下各商品的销售总额
SELECT
gt.cat_name,
IFNULL( sum( og.goods_number * og.goods_prices ), 0 ) amount
FROM
( ecs_goods g INNER JOIN ecs_goods_type gt ON g.goods_type = qt.cat_id )
LEFT JOIN ecs_order_goods og ON g.goods_id = og.goods_id
GROUP BY
gt.cat_name
IFNULL(sum(og.goods_number*og.goods_prices),0) 如果商品没有销售时，销售额显示为0
- 统计后过滤
-
- 统计每一个客户购物的总开销
SELECT
u.user_name,
IFNULL( sum( og.goods_numbers * og.goods_price ), 0 ) AS amount
FROM
( ecs_order_info oi INNER JOIN ecs_order_goods og ON oi.order_info = og.order_id )
RIGHT JOIN ecs_users u ON ou.user_id = u.user_id
GROUP BY
u.user_name;
-
- 哪些类型的商品平均价格超过了2000
SELECT
gt.cat_name,
AVG( g.market_price )
FROM
ecs_goods_type gt
LEFT JOIN ecs_goods g ON gt.cat_id = g.goods_type
GROUP BY
gt.cat_name
HAVING
AVG( g.market_price ) > 2000;
-
- 哪些类型的商品平均价格超过了所有产品均价 group by 与having
SELECT
gt.cat_name,
AVG( g.market_price )
FROM
ecs_goods_type gt
LEFT JOIN ecs_goods g ON gt.cat_id = g.goods_type
GROUP BY
gt.cat_name
HAVING
AVG( g.market_price ) > ( SELECT avg( market_price ) FROM ecs_goods );
-
- 列出总销售额超过10000的商品信息
SELECT
og.goods_name,
sum( og.goods_price * og.goods_number )
FROM
ecs_order_goods og
GROUP BY
og.goods_name
HAVING
sum( og.goods_price * og.goods_number ) > 10000;
-
- 有多少个订单只购买了一种商品
SELECT
count( * )
FROM
( SELECT order_id, count( goods_id ) FROM ecs_goods GROUP BY order_id HAVING count( goods_id ) = 1 ) t;#注意要给虚拟表加别名
4.DML
数据操作语言，插入，删除，更新数据库中的数据表
4.1 insert
- 插入一条记录
insert into 表名（c1,c2,c3...）
values（v1,v2,v3...）#顺序，类型，个数；插入的值要和列名顺序相对应
- 插入多条数据
insert into 表名（c1,c2,c3...）
values（v1,v2,v3...），
（v1,v2,v3...），
（v1,v2,v3...）；
- 不指定插入列，表名插入所有列
insert into 表名
values（v1,v2,v3...）
复制表:将a表中的数据复制到b表中
insert into b
select * from a
快速备份表
create table b
as select * from a;
4.2 update
语法
update tab_name
set col_name=new_value,col_name=new_value......
where search_condition;
修改用户zhangsan的密码和用户名
update ecs_users
set password='123345',qq='10000'
where user_name='zhangsan'
4.3 delete
语法：
delete from tab_name
where search_condition;
删除zhangsan用户
delete from ecs_users
where user_name='zhangsan';
参考链接：
https://study.163.com/course/courseMain.htm?courseId=1005821015