MySQL高级（进阶）SQL语句
一、实例准备--制表
1. 表一（商店区域表）
[root@localhost ~]# mysql
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Your MySQL connection id is 3
Server version: 5.7.20-log Source distribution
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owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> use test;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
Database changed
mysql> create table location (region char(20),store_name char(20));
Query OK, 0 rows affected (0.01 sec)
mysql> insert into location values('North','Beijing');
Query OK, 1 row affected (0.00 sec)
mysql> insert into location values('Eaet','shanghai');
Query OK, 1 row affected (0.00 sec)
mysql> insert into location values('South','Guangzhou');
Query OK, 1 row affected (0.00 sec)
mysql> insert into location values('South','Shenzhen');
Query OK, 1 row affected (0.01 sec)
mysql> select * from location;
+--------+------------+
| region | store_name |
+--------+------------+
| North | Beijing |
| East | Shanghai |
| South | Guangzhou |
| South | Shenzhen |
+--------+------------+
4 rows in set (0.00 sec)
2. 表2（商店销售表）
mysql> create table store_info (store_name char(20),sales int(10),date char(10));
Query OK, 0 rows affected (0.00 sec)
mysql> insert into store_info values('Guangzhou',1500,'2020-12-05');
Query OK, 1 row affected (0.00 sec)
mysql> insert into store_info values('Shenzhen',250,'2020-12-07');
Query OK, 1 row affected (0.00 sec)
mysql> insert into store_info values('Guangzhou',300,'2020-12-08');
Query OK, 1 row affected (0.00 sec)
mysql> insert into store_info values('Beijing',700,'2020-12-08');
Query OK, 1 row affected (0.00 sec)
mysql> select * from store_info;
+------------+-------+------------+
| store_name | sales | date |
+------------+-------+------------+
| Guangzhou | 1500 | 2020-12-05 |
| Shenzhen | 250 | 2020-12-07 |
| Guangzhou | 300 | 2020-12-08 |
| Beijing | 700 | 2020-12-08 |
+------------+-------+------------+
4 rows in set (0.00 sec)
3. 表3（城市表）
mysql> create table city(city_name char(20));
Query OK, 0 rows affected (0.00 sec)
mysql> insert into city values('beijing'),('nanjing'),('shanghai');
Query OK, 3 rows affected (0.01 sec)
Records: 3 Duplicates: 0 Warnings: 0
mysql> insert into city values();
Query OK, 1 row affected (0.00 sec)
mysql> insert into city values();
Query OK, 1 row affected (0.00 sec)
mysql> select * from city;
+-----------+
| city_name |
+-----------+
| beijing |
| nanjing |
| shanghai |
| NULL |
| NULL |
+-----------+
5 rows in set (0.00 sec)
二、SQL查询/匹配/排序语句
1. select
显示表格中一个或数个栏位的所有资料
语法：select "栏位" from "表名";
mysql> select store_name from store_info;
+------------+
| store_name |
+------------+
| Guangzhou |
| Shenzhen |
| Guangzhou |
| Beijing |
+------------+
4 rows in set (0.00 sec)
2. distinct
不显示重复的资料
语法：select dstinct "栏位" from "表名";
mysql> select distinct store_name from store_info;
+------------+
| store_name |
+------------+
| Guangzhou |
| Shenzhen |
| Beijing |
+------------+
3 rows in set (0.00 sec)
3. where
有条件查询
语法：select "栏位" from "表名" where "条件";
mysql> select store_name from store_info where sales>1000;
+------------+
| store_name |
+------------+
| Guangzhou |
+------------+
1 row in set (0.00 sec)
4. and|or
且、或
语法：select "栏位" from "表名" where "条件1" {[and|or] “条件2”}...;
mysql> select store_name from store_info where sales>1000 or (sales<500 and sales>200);
+------------+
| store_name |
+------------+
| Guangzhou |
| Shenzhen |
| Guangzhou |
+------------+
3 rows in set (0.00 sec)
5. in
显示已知的值的资料
语法：select "栏位" from "表名" where "栏位" in ("值1","值2",...);
mysql> select * from store_info where store_name in ('Beijing','Shenzhen');
+------------+-------+------------+
| store_name | sales | date |
+------------+-------+------------+
| Shenzhen | 250 | 2020-12-07 |
| Beijing | 700 | 2020-12-08 |
+------------+-------+------------+
2 rows in set (0.00 sec)
6. between
显示两个值范围内的资料
语法：select "栏位" from "表名" where "栏位" between '值1' and '值2';
mysql> select * from store_info where date between '2020-12-06' and '2020-12-10';
+------------+-------+------------+
| store_name | sales | date |
+------------+-------+------------+
| Shenzhen | 250 | 2020-12-07 |
| Guangzhou | 300 | 2020-12-08 |
| Beijing | 700 | 2020-12-08 |
+------------+-------+------------+
3 rows in set (0.00 sec)
7. limit
（1）显示前几行内容
语法：select "栏位" from "表名" limit '行数';
mysql> select * from store_info limit 2;
+------------+-------+------------+
| store_name | sales | date |
+------------+-------+------------+
| Guangzhou | 1500 | 2020-12-05 |
| Shenzhen | 250 | 2020-12-07 |
+------------+-------+------------+
2 rows in set (0.00 sec)
（2）显示第几行后的前几行
语法：select "栏位" from "表名" limit "第几行后,显示行数";
mysql> select * from store_info limit 2,2;
+------------+-------+------------+
| store_name | sales | date |
+------------+-------+------------+
| Guangzhou | 300 | 2020-12-08 |
| Beijing | 700 | 2020-12-08 |
+------------+-------+------------+
2 rows in set (0.00 sec)
8. 通配符
通常通配符都是跟like一起使用的
| 常用通配符 | 说明 |
|---|---|
| % | 百分号表示零个、一个或多个字符 |
| _ | 下划线表示单个字符 |
例如：
'A-Z'
表示所有以'A'起头，另一个任何值的字符，且以'Z'为结尾的字符串。例如，'ABZ'和'A2Z'都符合这一个模式，而'ABCZ'并不符合（因为A和Z之间有两个字符，而不是一个字符）
'ABC%'
表示所有以'ABC'起头的字符串。例如，'ABCD'和'ABCABC'都符合这个模式。
'%XYZ'
表示所有以'XYZ'结尾的字符串。例如，'WXYZ'和'ZZXYZ'都符合这个模式。
'%AN%'
表示所有含有'AN'这个模式的字符串。例如，'SHANGHAI'和'XIAN'都符合这个模式。
'_AN%'
表示第二个字母为'A'且第三个字母为'N'的字符串。例如，'HANGZHOU'和'LANZHOU'都符合这个模式，而'SHANGHAI'和'XIAN'则不符合这个模式。
9. like
匹配一个模式来搜查资料
语法：select "栏位" from “表名” where "栏位" like {模式};
mysql> select * from store_info where store_name like '%e%';
+------------+-------+------------+
| store_name | sales | date |
+------------+-------+------------+
| Shenzhen | 250 | 2020-12-07 |
| Beijing | 700 | 2020-12-08 |
+------------+-------+------------+
2 rows in set (0.00 sec)
10. order by
按关键字排序
语法：select "栏位" from “表名” [where "条件"] order by "栏位" [ASC,DESC];
ASC是按照升序进行排序的，是默认的排序方式。
DESC是按降序方式进行排序。
mysql> select store_name,sales,date from store_info order by sales desc;
+------------+-------+------------+
| store_name | sales | date |
+------------+-------+------------+
| Guangzhou | 1500 | 2020-12-05 |
| Beijing | 700 | 2020-12-08 |
| Guangzhou | 300 | 2020-12-08 |
| Shenzhen | 250 | 2020-12-07 |
+------------+-------+------------+
4 rows in set (0.00 sec)
三、函数
1. 数学函数
| 常用的数学函数 | 说明 |
|---|---|
| abs(x) | 返回x的绝对值 |
| rand() | 返回0-1的随机数 |
| mod(x,y) | 返回x除以y以后的余数 |
| power(x,y) | 返回x的y次方 |
| round(x) | 返回离x最近的整数，即四舍五入到个位 |
| round(x,y) | 返回x的y位小数且四舍五入后的值 |
| sqrt(x) | 返回x的平方根 |
| truncate(x,y) | 返回数字X截断为y位小数的值 |
| ceil(x) | 返回大于或等于x的最小整数 |
| floor(x) | 返回小于或等于x的最大整数 |
| greatest(x1,x2...) | 返回集合中最大的值 |
| least(x1,x2...) | 返回集合中最小的值 |
（1）abs(x)
返回x的绝对值
mysql> select abs(-2.3);
+-----------+
| abs(-2.3) |
+-----------+
| 2.3 |
+-----------+
1 row in set (0.00 sec)
（2）rand()
返回0-1的随机数
mysql> select rand();
+--------------------+
| rand() |
+--------------------+
| 0.1262695352791525 |
+--------------------+
1 row in set (0.00 sec)
（3）mod（x,y）
返回x除以y以后的余数
mysql> select mod(5,2);
+----------+
| mod(5,2) |
+----------+
| 1 |
+----------+
1 row in set (0.00 sec)
（4）power(x,y)
返回x的y次方
mysql> select power(2,8);
+------------+
| power(2,8) |
+------------+
| 256 |
+------------+
1 row in set (0.00 sec)
（5）round(x)
返回离x最近的整数,即四舍五入到个位
mysql> select round(3.1415);
+---------------+
| round(3.1415) |
+---------------+
| 3 |
+---------------+
1 row in set (0.00 sec)
mysql> select round(3.5415);
+---------------+
| round(3.5415) |
+---------------+
| 4 |
+---------------+
1 row in set (0.00 sec)
（6）round(x,y)
返回x的y位小数且四舍五入后的值
mysql> select round(3.1415,2);
+-----------------+
| round(3.1415,2) |
+-----------------+
| 3.14 |
+-----------------+
1 row in set (0.00 sec)
mysql> select round(3.1415,3);
+-----------------+
| round(3.1415,3) |
+-----------------+
| 3.142 |
+-----------------+
1 row in set (0.00 sec)
（7）sqrt(x)
返回x的平方根
mysql> select sqrt(9);
+---------+
| sqrt(9) |
+---------+
| 3 |
+---------+
1 row in set (0.00 sec)
mysql> select sqrt(8);
+--------------------+
| sqrt(8) |
+--------------------+
| 2.8284271247461903 |
+--------------------+
1 row in set (0.00 sec)
（8）truncate(x,y)
返回数字X截断为y位小数的值
mysql> select truncate(3.1415,2);
+--------------------+
| truncate(3.1415,2) |
+--------------------+
| 3.14 |
+--------------------+
1 row in set (0.00 sec)
mysql> select truncate(3.1415,3);
+--------------------+
| truncate(3.1415,3) |
+--------------------+
| 3.141 |
+--------------------+
1 row in set (0.00 sec)
（9）ceil(x)
返回大于或等于x的最小整数
mysql> select ceil(3.1415);
+--------------+
| ceil(3.1415) |
+--------------+
| 4 |
+--------------+
1 row in set (0.00 sec)
（10）floor(x)
返回小于或等于x的最大整数
mysql> select floor(3.1415);
+---------------+
| floor(3.1415) |
+---------------+
| 3 |
+---------------+
1 row in set (0.00 sec)
（11）greatest(x1,x2...)
返回集合中最大的值
mysql> select greatest(3.1415,3,4,5.2);
+--------------------------+
| greatest(3.1415,3,4,5.2) |
+--------------------------+
| 5.2000 |
+--------------------------+
1 row in set (0.00 sec)
（12）least(x1,x2...)
返回集合中最小的值
mysql> select least(3.1415,3,4,5.2);
+-----------------------+
| least(3.1415,3,4,5.2) |
+-----------------------+
| 3.0000 |
+-----------------------+
1 row in set (0.00 sec)
2. 聚合函数
| 常用的聚合函数 | 说明 |
|---|---|
| avg() | 返回指定列的平均值 |
| count() | 返回指定列中非NULL值的个数 |
| min() | 返回指定列的最小值 |
| max() | 返回指定列的最大值 |
| sum() | 返回指定列的所有值之和 |
（1）avg()
返回指定列的平均值
mysql> select avg(sales) from store_info;
+------------+
| avg(sales) |
+------------+
| 687.5000 |
+------------+
1 row in set (0.00 sec)
（2）count()
- 返回指定列中非NULL值的个数
mysql> select count(store_name) from store_info;
+-------------------+
| count(store_name) |
+-------------------+
| 4 |
+-------------------+
1 row in set (0.00 sec)
- 返回指定列中非NULL值且去重的个数
mysql> select count(distinct store_name) from store_info;
+----------------------------+
| count(distinct store_name) |
+----------------------------+
| 3 |
+----------------------------+
1 row in set (0.00 sec)
- count()
count()包括了所有的列的行数，在统计结果的时候，不会忽略值为NULL的行
mysql> select count(*) from city;
+----------+
| count(*) |
+----------+
| 5 |
+----------+
1 row in set (0.00 sec)
- count("列名")
count("列名")只包括列名那一列的行数，在统计结果的时候，会忽略值为NULL的行
mysql> select count(city_name) from city;
+------------------+
| count(city_name) |
+------------------+
| 3 |
+------------------+
1 row in set (0.00 sec)
（3）min()
返回指定列的最小值
mysql> select min(sales) from store_info;
+------------+
| min(sales) |
+------------+
| 250 |
+------------+
1 row in set (0.01 sec)
（4）max()
返回指定列的最大值
mysql> select max(sales) from store_info;
+------------+
| max(sales) |
+------------+
| 1500 |
+------------+
1 row in set (0.00 sec)
（5）sum()
返回指定列的所有值之和
mysql> select sum(sales) from store_info;
+------------+
| sum(sales) |
+------------+
| 2750 |
+------------+
1 row in set (0.00 sec)
3. 字符串函数
| 常用的字符串函数 | 说明 |
|---|---|
| trim() | 返回去除指定格式的值 |
| concat(x,y) | 将提供的参数x和y拼接成一个字符串 |
| substr(x,y) | 获取从字符串x中的第y个位置开始的字符串，跟substring()函数作用相同 |
| substr(x,y,z) | 获取从字符串x中第y个位置开始长度为z的字符串 |
| length(x) | 返回字符串x的长度 |
| replace(x,y,z) | 将字符串z替代字符串x中的字符串y |
| upper(x) | 将字符串x的所有字母变成大写字符 |
| lower(x) | 将字符串x的所有字母变成小写字符 |
| left(x,y) | 返回字符串x的前y个字符 |
| right(x,y) | 返回字符串x的后y个字符 |
| reprat(x,y) | 将字符串x重复y次 |
| space(x) | 返回x个空格 |
| strcmp(x,y) | 比较x和y，返回的值可以为-1,0,1 |
| reverse(x) | 将字符串x反转 |
（1）trim()
返回去除指定格式的值
语法：select trim([[位置] [要移除的字符串] from] 字符串);
[位置]：该值可以为leading（起头），trailing（结尾），both（起头及结尾）。缺省时为both。
[要移除的字符串]：从字串的起头、结尾，或起头即结尾移除的字符串。缺省时为空格。
mysql> select trim('g' from 'guangdong');
+----------------------------+
| trim('g' from 'guangdong') |
+----------------------------+
| uangdon |
+----------------------------+
1 row in set (0.00 sec)
mysql> select trim(leading 'g' from 'guangdong');
+------------------------------------+
| trim(leading 'g' from 'guangdong') |
+------------------------------------+
| uangdong |
+------------------------------------+
1 row in set (0.00 sec)
mysql> select trim(trailing 'g' from 'guangdong');
+-------------------------------------+
| trim(trailing 'g' from 'guangdong') |
+-------------------------------------+
| guangdon |
+-------------------------------------+
1 row in set (0.00 sec)
mysql> select trim(both 'g' from 'guangdong');
+---------------------------------+
| trim(both 'g' from 'guangdong') |
+---------------------------------+
| uangdon |
+---------------------------------+
1 row in set (0.00 sec)
（2）concat(x,y)
将提供的参数x和y拼接成一个字符串
mysql> select concat (region,' ',store_name) from location where store_name='Beeijing';
+--------------------------------+
| concat (region,' ',store_name) |
+--------------------------------+
| North Beijing |
+--------------------------------+
1 row in set (0.00 sec)
如sql_mode开启了PIPES_AS_CONCAT（可使用"select @@SESSION.sql_mode;"或"select @@GLOBAL.sql_mode;"进行查看），"||"视为字符串的连接操作符而非或运算符，和字符串的拼接函数相类似，这和Oracle数据库使用方法一样。
mysql> select store_name || ' ' || sales from store_info where store_name='Guanngzhou';
+----------------------------+
| store_name || ' ' || sales |
+----------------------------+
| Guangzhou 1500 |
| Guangzhou 300 |
+----------------------------+
2 rows in set (0.00 sec)
（3）substr(x,y)
获取从字符串x中的第y个位置开始的字符串，跟substring()函数作用相同
mysql> select substr(store_name,3) from location where store_name='Guangzhou';
+----------------------+
| substr(store_name,3) |
+----------------------+
| angzhou |
+----------------------+
1 row in set (0.00 sec)
（4）substr(x,y,z)
获取从字符串x中第y个位置开始长度为z的字符串
mysql> select substr(store_name,3,4) from location where store_name='Guangzhou'';
+------------------------+
| substr(store_name,3,4) |
+------------------------+
| angz |
+------------------------+
1 row in set (0.00 sec)
（5）length(x)
返回字符串x的长度
mysql> select *,length(store_name) from location;
+--------+------------+--------------------+
| region | store_name | length(store_name) |
+--------+------------+--------------------+
| North | Beijing | 7 |
| East | Shanghai | 8 |
| South | Guangzhou | 9 |
| South | Shenzhen | 8 |
+--------+------------+--------------------+
4 rows in set (0.00 sec)
（6）replace(x,y,z)
将字符串z替代字符串x中的字符串y
mysql> select replace(store_name,'ng','xx') from location;
+-------------------------------+
| replace(store_name,'ng','xx') |
+-------------------------------+
| Beijixx |
| Shaxxhai |
| Guaxxzhou |
| Shenzhen |
+-------------------------------+
4 rows in set (0.00 sec)
（7）upper(x)
将字符串x的所有字母变成大写字符
mysql> select upper(store_name) from location;
+-------------------+
| upper(store_name) |
+-------------------+
| BEIJING |
| SHANGHAI |
| GUANGZHOU |
| SHENZHEN |
+-------------------+
4 rows in set (0.00 sec)
（8）lower(x)
将字符串x的所有字母变成小写字符
mysql> select lower(store_name) from location;
+-------------------+
| lower(store_name) |
+-------------------+
| beijing |
| shanghai |
| guangzhou |
| shenzhen |
+-------------------+
4 rows in set (0.00 sec)
（9）left(x,y)
返回字符串x的前y个字符
mysql> select left('Beijing',3);
+-------------------+
| left('Beijing',3) |
+-------------------+
| Bei |
+-------------------+
1 row in set (0.00 sec)
（10）right(x,y)
返回字符串x的后y个字符
mysql> select right('Beijing',3);
+--------------------+
| right('Beijing',3) |
+--------------------+
| ing |
+--------------------+
1 row in set (0.00 sec)
（11）reprat(x,y)
将字符串x重复y次
mysql> select repeat('Beijing ',3);
+--------------------------+
| repeat('Beijing ',3) |
+--------------------------+
| Beijing Beijing Beijing |
+--------------------------+
1 row in set (0.00 sec)
（12）space(x)
返回x个空格
mysql> select space(10);
+------------+
| space(10) |
+------------+
| |
+------------+
1 row in set (0.00 sec)
mysql> select space(15);
+-----------------+
| space(15) |
+-----------------+
| |
+-----------------+
1 row in set (0.00 sec)
（13）strcmp(x,y)
比较x和y，返回的值可以为-1,0,1
x=y，返回0
mysql> select strcmp(1,1);
+-------------+
| strcmp(1,1) |
+-------------+
| 0 |
+-------------+
1 row in set (0.00 sec)
x<y，返回-1
mysql> select strcmp(1,2);
+-------------+
| strcmp(1,2) |
+-------------+
| -1 |
+-------------+
1 row in set (0.00 sec)
x>y，返回1
mysql> select strcmp(2,1);
+-------------+
| strcmp(2,1) |
+-------------+
| 1 |
+-------------+
1 row in set (0.00 sec)
（14）reverse(x)
将字符串x反转
mysql> select reverse(sales) from store_info;
+----------------+
| reverse(sales) |
+----------------+
| 0051 |
| 052 |
| 003 |
| 007 |
+----------------+
4 rows in set (0.00 sec)
四、分组
1. group by
对group by后面的栏位的查询结果进行汇总分组，通常是结合聚合函数一起使用的。
group by有一个原则，就是select后面的所有列中，没有使用聚合函数的列，必须出现在group by 后面。
语法：select "栏位1",sum("栏位2") from "表名" group by "栏位1";
mysql> select store_name,sum(sales) from store_info group by store_name order by sales desc;
+------------+------------+
| store_name | sum(sales) |
+------------+------------+
| Guangzhou | 1800 |
| Beijing | 700 |
| Shenzhen | 250 |
+------------+------------+
3 rows in set (0.00 sec)
"Guangzhou"有两条属性信息，通过group by分组后，同名项将被合并，可通过以下方式确定是否有重名项以及重名次数。
mysql> select store_name,count(store_name),sum(sales) from store_info group by store_name order by sales desc;
+------------+-------------------+------------+
| store_name | count(store_name) | sum(sales) |
+------------+-------------------+------------+
| Guangzhou | 2 | 1800 |
| Beijing | 1 | 700 |
| Shenzhen | 1 | 250 |
+------------+-------------------+------------+
3 rows in set (0.00 sec)
也可通过前后sales是否变化，判断是否有重名项被合并。
mysql> select store_name,sales,sum(sales) from store_info group by store_name order by sales desc;
+------------+-------+------------+
| store_name | sales | sum(sales) |
+------------+-------+------------+
| Guangzhou | 1500 | 1800 |
| Beijing | 700 | 700 |
| Shenzhen | 250 | 250 |
+------------+-------+------------+
3 rows in set (0.00 sec)
2. having
用来过滤由group by语句返回的记录集，通常与group by语句联合使用。
having语句的存在弥补了where关键字不能与聚合函数联合使用的不足。如果被select的只有函数栏，那就不需要group by子句。
语法：select "栏位1",sum("栏位2") from "表名" group by “栏位1” having (函数条件);
mysql> select store_name,sum(sales) from store_info group by store_name having sum(sales)>1500;
+------------+------------+
| store_name | sum(sales) |
+------------+------------+
| Guangzhou | 1800 |
+------------+------------+
1 row in set (0.00 sec)
五、别名
栏位别名/表格别名
语法：select "表格别名"."栏位1" [as] "栏位别名" from "表格名" [as] "表格别名";
mysql> select A.store_name as STORE,sum(A.sales) as 'TOTAL_SALES' from store_info as A group by STORE;
+-----------+-------------+
| STORE | TOTAL_SALES |
+-----------+-------------+
| Beijing | 700 |
| Guangzhou | 1800 |
| Shenzhen | 250 |
+-----------+-------------+
3 rows in set (0.00 sec)
六、子查询
连接表格，在where子句或having子句中插入另一个SQL语句
语法：slect "栏位1" from "表格1" where "栏位2" [比较运算符] (select "栏位1" from "表格2" where "条件");
其中：
slect "栏位1" from "表格1" where "栏位2" [比较运算符] 为外查询，
(select "栏位1" from "表格2" where "条件")为内查询。
[比较运算符]可以是符号的运算符，例如=、>、<、>=、<=；也可以是文字的匹配符，例如like、in、between等。
mysql> select sum(sales) from store_info where store_name in (select store_name from location where region='North');
+------------+
| sum(sales) |
+------------+
| 700 |
+------------+
1 row in set (0.00 sec)
注：匹配两个表的列名可以不相同，但列中需有相同内容，否则将返回空值。
mysql> alter table location change store_name name char(20);
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> select sum(sales) from store_info where store_name in (select name from location where region='North');
+------------+
| sum(sales) |
+------------+
| 700 |
+------------+
1 row in set (0.00 sec)
mysql> select sum(sales) from store_info where sales in (select name from locattion where region='North');
+------------+
| sum(sales) |
+------------+
| NULL |
+------------+
1 row in set, 4 warnings (0.00 sec)
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