三 查询知识
注:以下查询基于ecshop网站的商品表(ecs_goods)
在练习时可以只取部分列,方便查看.
1: 基础查询 where的练习:
查出满足以下条件的商品
1.1:主键为32的商品
select goods_id,goods_name,shop_price
from ecs_goods
where goods_id=32;
1.2:不属第3栏目的所有商品
select goods_id,cat_id,goods_name,shop_price from ecs_goods
where cat_id!=3;
1.3:本店价格高于3000元的商品
select goods_id,cat_id,goods_name,shop_price from ecs_goods
where shop_price >3000;
1.4:本店价格低于或等于100元的商品
select goods_id,cat_id,goods_name,shop_price from ecs_goods where shop_price <=100;
1.5:取出第4栏目或第11栏目的商品(不许用or)
select goods_id,cat_id,goods_name,shop_price from ecs_goods
where cat_id in (4,11);
1.6:取出100<=价格<=500的商品(不许用and)
select goods_id,cat_id,goods_name,shop_price from ecs_goods
where shop_price between 100 and 500;
1.7:取出不属于第3栏目且不属于第11栏目的商品(and,或not in分别实现)
select goods_id,cat_id,goods_name,shop_price from ecs_goods where cat_id!=3 and cat_id!=11;
select goods_id,cat_id,goods_name,shop_price from ecs_goods where cat_id not in (3,11);
1.8:取出价格大于100且小于300,或者大于4000且小于5000的商品()
select goods_id,cat_id,goods_name,shop_price from ecs_goods where shop_price>100 and shop_price <300 or shop_price >4000 and shop_price <5000;
1.9:取出第3个栏目下面价格<1000或>3000,并且点击量>5的系列商品
select goods_id,cat_id,goods_name,shop_price,click_count from ecs_goods where
cat_id=3 and (shop_price <1000 or shop_price>3000) and click_count>5;
1.10:取出第1个栏目下面的商品(注意:1栏目下面没商品,但其子栏目下有)
select goods_id,cat_id,goods_name,shop_price,click_count from ecs_goods
where cat_id in (2,3,4,5);
1.11:取出名字以"诺基亚"开头的商品
select goods_id,cat_id,goods_name,shop_price from ecs_goods where goods_name like '诺基亚%';
1.12:取出名字为"诺基亚Nxx"的手机
select goods_id,cat_id,goods_name,shop_price from ecs_goods
where goods_name like '诺基亚N__';
1.13:取出名字不以"诺基亚"开头的商品
select goods_id,cat_id,goods_name,shop_price from ecs_goos
where goods_name not like '诺基亚%';
1.14:取出第3个栏目下面价格在1000到3000之间,并且点击量>5 "诺基亚"开头的系列商品
select goods_id,cat_id,goods_name,shop_price from ecs_goods where
cat_id=3 and shop_price>1000 and shop_price <3000 and click_count>5 and goods_name like '诺基亚%';
select goods_id,cat_id,goods_name,shop_price from ecs_goods where
shop_price between 1000 and 3000 and cat_id=3 and click_count>5 and goods_name like '诺基亚%';
一道面试题
有如下表和数组
把num值处于[20,29]之间,改为20
num值处于[30,39]之间的,改为30
mian表
+------+
| num |
+------+
| 3 |
| 12 |
| 15 |
| 25 |
| 23 |
| 29 |
| 34 |
| 37 |
| 32 |
| 45 |
| 48 |
| 52 |
+------+
练习题:
把good表中商品名为'诺基亚xxxx'的商品,改为'HTCxxxx',
提示:大胆的把列看成变量,参与运算,甚至调用函数来处理 .
substring(),concat()
2 分组查询group:
2.1:查出最贵的商品的价格
select max(shop_price) from ecs_goods;
2.2:查出最大(最新)的商品编号
select max(goods_id) from ecs_goods;
2.3:查出最便宜的商品的价格
select min(shop_price) from ecs_goods;
2.4:查出最旧(最小)的商品编号
select min(goods_id) from ecs_goods;
2.5:查询该店所有商品的库存总量
select sum(goods_number) from ecs_goods;
2.6:查询所有商品的平均价
select avg(shop_price) from ecs_goods;
2.7:查询该店一共有多少种商品
select count(*) from ecs_goods;
2.8:查询每个栏目下面
最贵商品价格
最低商品价格
商品平均价格
商品库存量
商品种类
提示:(5个聚合函数,sum,avg,max,min,count与group综合运用)
select cat_id,max(shop_price) from ecs_goods group by cat_id;
3 having与group综合运用查询:
3.1:查询该店的商品比市场价所节省的价格
select goods_id,goods_name,market_price-shop_price as j
from ecs_goods ;
3.2:查询每个商品所积压的货款(提示:库存*单价)
select goods_id,goods_name,goods_number*shop_price from ecs_goods
3.3:查询该店积压的总货款
select sum(goods_number*shop_price) from ecs_goods;
3.4:查询该店每个栏目下面积压的货款.
select cat_id,sum(goods_number*shop_price) as k from ecs_goods group by cat_id;
3.5:查询比市场价省钱200元以上的商品及该商品所省的钱(where和having分别实现)
select goods_id,goods_name,market_price-shop_price as k from ecs_goods
where market_price-shop_price >200;
select goods_id,goods_name,market_price-shop_price as k from ecs_goods
having k >200;
3.6:查询积压货款超过2W元的栏目,以及该栏目积压的货款
select cat_id,sum(goods_number*shop_price) as k from ecs_goods group by cat_id
having k>20000
3.7:where-having-group综合练习题
有如下表及数据
+------+---------+-------+
| name | subject | score |
+------+---------+-------+
| 张三 | 数学 | 90 |
| 张三 | 语文 | 50 |
| 张三 | 地理 | 40 |
| 李四 | 语文 | 55 |
| 李四 | 政治 | 45 |
| 王五 | 政治 | 30 |
+------+---------+-------+
要求:查询出2门及2门以上不及格者的平均成绩
## 一种错误做法
mysql> select name,count(score<60) as k,avg(score) from stu group by name having k>=2;
+------+---+------------+
| name | k | avg(score) |
+------+---+------------+
| 张三 | 3 | 60.0000 |
| 李四 | 2 | 50.0000 |
+------+---+------------+
2 rows in set (0.00 sec)
mysql> select name,count(score<60) as k,avg(score) from stu group by name;
+------+---+------------+
| name | k | avg(score) |
+------+---+------------+
| 张三 | 3 | 60.0000 |
| 李四 | 2 | 50.0000 |
| 王五 | 1 | 30.0000 |
+------+---+------------+
3 rows in set (0.00 sec)
mysql> select name,count(score<60) as k,avg(score) from stu group by name having k>=2;
+------+---+------------+
| name | k | avg(score) |
+------+---+------------+
| 张三 | 3 | 60.0000 |
| 李四 | 2 | 50.0000 |
+------+---+------------+
2 rows in set (0.00 sec)
#加上赵六后错误暴露
mysql> insert into stu
-> values
-> ('赵六','A',100),
-> ('赵六','B',99),
-> ('赵六','C',98);
Query OK, 3 rows affected (0.05 sec)
Records: 3 Duplicates: 0 Warnings: 0
#错误显现
mysql> select name,count(score<60) as k,avg(score) from stu group by name having k>=2;
+------+---+------------+
| name | k | avg(score) |
+------+---+------------+
| 张三 | 3 | 60.0000 |
| 李四 | 2 | 50.0000 |
| 赵六 | 3 | 99.0000 |
+------+---+------------+
3 rows in set (0.00 sec)
#正确思路,先查看每个人的平均成绩
mysql> select name,avg(score) from stu group by name;
+------+------------+
| name | avg(score) |
+------+------------+
| 张三 | 60.0000 |
| 李四 | 50.0000 |
| 王五 | 30.0000 |
| 赵六 | 99.0000 |
+------+------------+
4 rows in set (0.00 sec)
mysql> # 看每个人挂科情况
mysql> select name,score < 60 from stu;
+------+------------+
| name | score < 60 |
+------+------------+
| 张三 | 0 |
| 张三 | 1 |
| 张三 | 1 |
| 李四 | 1 |
| 李四 | 1 |
| 王五 | 1 |
| 赵六 | 0 |
| 赵六 | 0 |
| 赵六 | 0 |
+------+------------+
9 rows in set (0.00 sec)
mysql> #计算每个人的挂科科目
mysql> select name,sum(score < 60) from stu group by name;
+------+-----------------+
| name | sum(score < 60) |
+------+-----------------+
| 张三 | 2 |
| 李四 | 2 |
| 王五 | 1 |
| 赵六 | 0 |
+------+-----------------+
4 rows in set (0.00 sec)
#同时计算每人的平均分
mysql> select name,sum(score < 60),avg(score) as pj from stu group by name;
+------+-----------------+---------+
| name | sum(score < 60) | pj |
+------+-----------------+---------+
| 张三 | 2 | 60.0000 |
| 李四 | 2 | 50.0000 |
| 王五 | 1 | 30.0000 |
| 赵六 | 0 | 99.0000 |
+------+-----------------+---------+
4 rows in set (0.00 sec)
#利用having筛选挂科2门以上的.
mysql> select name,sum(score < 60) as gk ,avg(score) as pj from stu group by name having gk >=2;
+------+------+---------+
| name | gk | pj |
+------+------+---------+
| 张三 | 2 | 60.0000 |
| 李四 | 2 | 50.0000 |
+------+------+---------+
2 rows in set (0.00 sec)
4: order by 与 limit查询
4.1:按价格由高到低排序
select goods_id,goods_name,shop_price from ecs_goods order by shop_price desc;
4.2:按发布时间由早到晚排序
select goods_id,goods_name,add_time from ecs_goods order by add_time;
4.3:接栏目由低到高排序,栏目内部按价格由高到低排序
select goods_id,cat_id,goods_name,shop_price from ecs_goods
order by cat_id ,shop_price desc;
4.4:取出价格最高的前三名商品
select goods_id,goods_name,shop_price from ecs_goods order by shop_price desc limit 3;
4.5:取出点击量前三名到前5名的商品
select goods_id,goods_name,click_count from ecs_goods order by click_count desc limit 2,3;
5 连接查询
5.1:取出所有商品的商品名,栏目名,价格
select goods_name,cat_name,shop_price from
ecs_goods left join ecs_category
on ecs_goods.cat_id=ecs_category.cat_id;
5.2:取出第4个栏目下的商品的商品名,栏目名,价格
select goods_name,cat_name,shop_price from
ecs_goods left join ecs_category
on ecs_goods.cat_id=ecs_category.cat_id
where ecs_goods.cat_id = 4;
5.3:取出第4个栏目下的商品的商品名,栏目名,与品牌名
select goods_name,cat_name,brand_name from
ecs_goods left join ecs_category
on ecs_goods.cat_id=ecs_category.cat_id
left join ecs_brand
on ecs_goods.brand_id=ecs_brand.brand_id
where ecs_goods.cat_id = 4;
注:以下查询基于ecshop网站的商品表(ecs_goods)
在练习时可以只取部分列,方便查看.
1: 基础查询 where的练习:
查出满足以下条件的商品
1.1:主键为32的商品
select goods_id,goods_name,shop_price
from ecs_goods
where goods_id=32;
1.2:不属第3栏目的所有商品
select goods_id,cat_id,goods_name,shop_price from ecs_goods
where cat_id!=3;
1.3:本店价格高于3000元的商品
select goods_id,cat_id,goods_name,shop_price from ecs_goods
where shop_price >3000;
1.4:本店价格低于或等于100元的商品
select goods_id,cat_id,goods_name,shop_price from ecs_goods where shop_price <=100;
1.5:取出第4栏目或第11栏目的商品(不许用or)
select goods_id,cat_id,goods_name,shop_price from ecs_goods
where cat_id in (4,11);
1.6:取出100<=价格<=500的商品(不许用and)
select goods_id,cat_id,goods_name,shop_price from ecs_goods
where shop_price between 100 and 500;
1.7:取出不属于第3栏目且不属于第11栏目的商品(and,或not in分别实现)
select goods_id,cat_id,goods_name,shop_price from ecs_goods where cat_id!=3 and cat_id!=11;
select goods_id,cat_id,goods_name,shop_price from ecs_goods where cat_id not in (3,11);
1.8:取出价格大于100且小于300,或者大于4000且小于5000的商品()
select goods_id,cat_id,goods_name,shop_price from ecs_goods where shop_price>100 and shop_price <300 or shop_price >4000 and shop_price <5000;
1.9:取出第3个栏目下面价格<1000或>3000,并且点击量>5的系列商品
select goods_id,cat_id,goods_name,shop_price,click_count from ecs_goods where
cat_id=3 and (shop_price <1000 or shop_price>3000) and click_count>5;
1.10:取出第1个栏目下面的商品(注意:1栏目下面没商品,但其子栏目下有)
select goods_id,cat_id,goods_name,shop_price,click_count from ecs_goods
where cat_id in (2,3,4,5);
1.11:取出名字以"诺基亚"开头的商品
select goods_id,cat_id,goods_name,shop_price from ecs_goods where goods_name like '诺基亚%';
1.12:取出名字为"诺基亚Nxx"的手机
select goods_id,cat_id,goods_name,shop_price from ecs_goods
where goods_name like '诺基亚N__';
1.13:取出名字不以"诺基亚"开头的商品
select goods_id,cat_id,goods_name,shop_price from ecs_goos
where goods_name not like '诺基亚%';
1.14:取出第3个栏目下面价格在1000到3000之间,并且点击量>5 "诺基亚"开头的系列商品
select goods_id,cat_id,goods_name,shop_price from ecs_goods where
cat_id=3 and shop_price>1000 and shop_price <3000 and click_count>5 and goods_name like '诺基亚%';
select goods_id,cat_id,goods_name,shop_price from ecs_goods where
shop_price between 1000 and 3000 and cat_id=3 and click_count>5 and goods_name like '诺基亚%';
一道面试题
有如下表和数组
把num值处于[20,29]之间,改为20
num值处于[30,39]之间的,改为30
mian表
+------+
| num |
+------+
| 3 |
| 12 |
| 15 |
| 25 |
| 23 |
| 29 |
| 34 |
| 37 |
| 32 |
| 45 |
| 48 |
| 52 |
+------+
练习题:
把good表中商品名为'诺基亚xxxx'的商品,改为'HTCxxxx',
提示:大胆的把列看成变量,参与运算,甚至调用函数来处理 .
substring(),concat()
2 分组查询group:
2.1:查出最贵的商品的价格
select max(shop_price) from ecs_goods;
2.2:查出最大(最新)的商品编号
select max(goods_id) from ecs_goods;
2.3:查出最便宜的商品的价格
select min(shop_price) from ecs_goods;
2.4:查出最旧(最小)的商品编号
select min(goods_id) from ecs_goods;
2.5:查询该店所有商品的库存总量
select sum(goods_number) from ecs_goods;
2.6:查询所有商品的平均价
select avg(shop_price) from ecs_goods;
2.7:查询该店一共有多少种商品
select count(*) from ecs_goods;
2.8:查询每个栏目下面
最贵商品价格
最低商品价格
商品平均价格
商品库存量
商品种类
提示:(5个聚合函数,sum,avg,max,min,count与group综合运用)
select cat_id,max(shop_price) from ecs_goods group by cat_id;
3 having与group综合运用查询:
3.1:查询该店的商品比市场价所节省的价格
select goods_id,goods_name,market_price-shop_price as j
from ecs_goods ;
3.2:查询每个商品所积压的货款(提示:库存*单价)
select goods_id,goods_name,goods_number*shop_price from ecs_goods
3.3:查询该店积压的总货款
select sum(goods_number*shop_price) from ecs_goods;
3.4:查询该店每个栏目下面积压的货款.
select cat_id,sum(goods_number*shop_price) as k from ecs_goods group by cat_id;
3.5:查询比市场价省钱200元以上的商品及该商品所省的钱(where和having分别实现)
select goods_id,goods_name,market_price-shop_price as k from ecs_goods
where market_price-shop_price >200;
select goods_id,goods_name,market_price-shop_price as k from ecs_goods
having k >200;
3.6:查询积压货款超过2W元的栏目,以及该栏目积压的货款
select cat_id,sum(goods_number*shop_price) as k from ecs_goods group by cat_id
having k>20000
3.7:where-having-group综合练习题
有如下表及数据
+------+---------+-------+
| name | subject | score |
+------+---------+-------+
| 张三 | 数学 | 90 |
| 张三 | 语文 | 50 |
| 张三 | 地理 | 40 |
| 李四 | 语文 | 55 |
| 李四 | 政治 | 45 |
| 王五 | 政治 | 30 |
+------+---------+-------+
要求:查询出2门及2门以上不及格者的平均成绩
## 一种错误做法
mysql> select name,count(score<60) as k,avg(score) from stu group by name having k>=2;
+------+---+------------+
| name | k | avg(score) |
+------+---+------------+
| 张三 | 3 | 60.0000 |
| 李四 | 2 | 50.0000 |
+------+---+------------+
2 rows in set (0.00 sec)
mysql> select name,count(score<60) as k,avg(score) from stu group by name;
+------+---+------------+
| name | k | avg(score) |
+------+---+------------+
| 张三 | 3 | 60.0000 |
| 李四 | 2 | 50.0000 |
| 王五 | 1 | 30.0000 |
+------+---+------------+
3 rows in set (0.00 sec)
mysql> select name,count(score<60) as k,avg(score) from stu group by name having k>=2;
+------+---+------------+
| name | k | avg(score) |
+------+---+------------+
| 张三 | 3 | 60.0000 |
| 李四 | 2 | 50.0000 |
+------+---+------------+
2 rows in set (0.00 sec)
#加上赵六后错误暴露
mysql> insert into stu
-> values
-> ('赵六','A',100),
-> ('赵六','B',99),
-> ('赵六','C',98);
Query OK, 3 rows affected (0.05 sec)
Records: 3 Duplicates: 0 Warnings: 0
#错误显现
mysql> select name,count(score<60) as k,avg(score) from stu group by name having k>=2;
+------+---+------------+
| name | k | avg(score) |
+------+---+------------+
| 张三 | 3 | 60.0000 |
| 李四 | 2 | 50.0000 |
| 赵六 | 3 | 99.0000 |
+------+---+------------+
3 rows in set (0.00 sec)
#正确思路,先查看每个人的平均成绩
mysql> select name,avg(score) from stu group by name;
+------+------------+
| name | avg(score) |
+------+------------+
| 张三 | 60.0000 |
| 李四 | 50.0000 |
| 王五 | 30.0000 |
| 赵六 | 99.0000 |
+------+------------+
4 rows in set (0.00 sec)
mysql> # 看每个人挂科情况
mysql> select name,score < 60 from stu;
+------+------------+
| name | score < 60 |
+------+------------+
| 张三 | 0 |
| 张三 | 1 |
| 张三 | 1 |
| 李四 | 1 |
| 李四 | 1 |
| 王五 | 1 |
| 赵六 | 0 |
| 赵六 | 0 |
| 赵六 | 0 |
+------+------------+
9 rows in set (0.00 sec)
mysql> #计算每个人的挂科科目
mysql> select name,sum(score < 60) from stu group by name;
+------+-----------------+
| name | sum(score < 60) |
+------+-----------------+
| 张三 | 2 |
| 李四 | 2 |
| 王五 | 1 |
| 赵六 | 0 |
+------+-----------------+
4 rows in set (0.00 sec)
#同时计算每人的平均分
mysql> select name,sum(score < 60),avg(score) as pj from stu group by name;
+------+-----------------+---------+
| name | sum(score < 60) | pj |
+------+-----------------+---------+
| 张三 | 2 | 60.0000 |
| 李四 | 2 | 50.0000 |
| 王五 | 1 | 30.0000 |
| 赵六 | 0 | 99.0000 |
+------+-----------------+---------+
4 rows in set (0.00 sec)
#利用having筛选挂科2门以上的.
mysql> select name,sum(score < 60) as gk ,avg(score) as pj from stu group by name having gk >=2;
+------+------+---------+
| name | gk | pj |
+------+------+---------+
| 张三 | 2 | 60.0000 |
| 李四 | 2 | 50.0000 |
+------+------+---------+
2 rows in set (0.00 sec)
4: order by 与 limit查询
4.1:按价格由高到低排序
select goods_id,goods_name,shop_price from ecs_goods order by shop_price desc;
4.2:按发布时间由早到晚排序
select goods_id,goods_name,add_time from ecs_goods order by add_time;
4.3:接栏目由低到高排序,栏目内部按价格由高到低排序
select goods_id,cat_id,goods_name,shop_price from ecs_goods
order by cat_id ,shop_price desc;
4.4:取出价格最高的前三名商品
select goods_id,goods_name,shop_price from ecs_goods order by shop_price desc limit 3;
4.5:取出点击量前三名到前5名的商品
select goods_id,goods_name,click_count from ecs_goods order by click_count desc limit 2,3;
5 连接查询
5.1:取出所有商品的商品名,栏目名,价格
select goods_name,cat_name,shop_price from
ecs_goods left join ecs_category
on ecs_goods.cat_id=ecs_category.cat_id;
5.2:取出第4个栏目下的商品的商品名,栏目名,价格
select goods_name,cat_name,shop_price from
ecs_goods left join ecs_category
on ecs_goods.cat_id=ecs_category.cat_id
where ecs_goods.cat_id = 4;
5.3:取出第4个栏目下的商品的商品名,栏目名,与品牌名
select goods_name,cat_name,brand_name from
ecs_goods left join ecs_category
on ecs_goods.cat_id=ecs_category.cat_id
left join ecs_brand
on ecs_goods.brand_id=ecs_brand.brand_id
where ecs_goods.cat_id = 4;
