MySQL高级SQL语句

MySQL高级SQL语句

围绕两张表

Location表

Store_Info表

 #select选择
 SELECT Store_Name FROM Store_Info;
 #distinct去重
 select distinct 列名 from 表名
 #where条件查询
 select distinct 列名 from 表名 where
 #and且  or或
 语法：SELECT "字段" FROM "表名" WHERE "条件1" {[AND|OR] "条件2"}+ ;
 SELECT Store_Name FROM Store_Info WHERE Sales > 1000 OR (Sales < 500 AND Sales > 200);
 #in显示已知的
 not in ≈取反
 语法：SELECT "字段" FROM "表名" WHERE "字段" IN ('值1', '值2', ...);
 SELECT * FROM Store_Info WHERE Store_Name IN ('Los Angeles', 'Houston');
 #between两个值范围内的数据记录
 select * from store_info where between 300 and 1000;
 300≤结果≤1000
 ​
 #通配符——配合like使用
 %：百分号表示零个、一个或多个字符
 _：下划线表示单个字符
 ​
 #like
 语法：SELECT "字段" FROM "表名" WHERE "字段" LIKE {模式};
 SELECT * FROM Store_Info WHERE Store_Name like '%os%';
 ​
 #order by
 asc升序
 desc降序
 语法：SELECT "字段" FROM "表名" [WHERE "条件"] ORDER BY "字段" [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。
 SELECT Store_Name,Sales,Date FROM Store_Info ORDER BY Sales DESC;

 函数
 数学函数：
 abs(x)              返回 x 的绝对值
 rand()              返回 0 到 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
 round(x,y)          保留 x 的 y 位小数四舍五入后的值
 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，也可以返回多个字段的最大的值
 least(x1,x2...)     返回集合中最小的值，也可以返回多个字段的最小的值
 SELECT abs(-1), rand(), mod(5,3), power(2,3), round(1.89);
 SELECT round(1.8937,3), truncate(1.235,2), ceil(5.2), floor(2.1), least(1.89,3,6.1,2.1);
 ​
 聚合函数：
 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(x)              返回指定列的所有值之和
 ​
 SELECT avg(Sales) FROM Store_Info;
 ​
 SELECT count(Store_Name) FROM Store_Info;
 SELECT count(DISTINCT Store_Name) FROM Store_Info;
 ​
 SELECT max(Sales) FROM Store_Info;
 SELECT min(Sales) FROM Store_Info;
 ​
 SELECT sum(Sales) FROM Store_Info;

 字符串函数
 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 中的第 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母
 lower(x)            将字符串 x 的所有字母变成小写字母
 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
 repeat(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
 ​

 a=12345678
 echo $(a:6:3)
 echo $(#a)

 GROUP BY配合“聚合函数”一起使用
 ​
 HAVING 对group by汇总后的结果做筛选

select store_name ,sum(store_name) from store_info group by store_name having sum(store_name) >=2

连接查询

 ​
 select * from location as A inner join store_info as B on A.store_name = B.store_name;
 ​

表连接

inner join 内连接，只返回两个表的字段相等的行记录

left join 左连接，返回左表所有的行记录和右表字段相等的行记录，不相等的行返回null

right join 右连接，返回右表所有的行记录和左表字段相等的行记录，不相等的行返回null

union 联集，将两个select查询语句的结果合并，并去重

union all 联集，将两个select查询语句的结果合并，不去重

求交集

select A.字段 from 左表 A inner join 右表 B

 数据库模式：
 create database kgc;
 ​
 show databases;
 ​
 use kgc;
 ​
 create table location (Region char(20),Store_Name char(20));
 ​
 desc location;
 ​
 insert into location values('East','Boston');
 insert into location values('East','New York');
 insert into location values('West','Los Angeles');
 insert into location values('West','Houston');
 ​
 select * from location;
 ​
 create table store_info (Store_Name char(20),Sales int(10),Date char(10));
 desc store_info;
 ​
 insert into store_info values('Los Angeles','1500','2020-12-05');
 insert into store_info values('Houston','250','2020-12-07');
 insert into store_info values('Los Angeles','300','2020-12-08');
 insert into store_info values('Boston','700','2020-12-08');
 ​
 select * from store_info;
 ​
 select * from store_info where store_name='Los Angeles';
 ​
 select * from store_info where sales <= 1000;
 ​
 select * from store_info where sales >= 1000;
 ​
 select * from store_info where sales != 1500;
 ​
 select * from store_info where sales > 1000 or (sales < 500 and sales > 200);
 ​
 select * from store_info where Store_Name in ('Los Angeles', 'Houston');
 ​
 select * from store_info where date between '2020-12-06' and '2020-12-10';
 ​
 select * from store_info where store_name like '%os%';
 ​
 select store_name,sales,date from store_info order by sales desc;
 ​
 select sum(sales) from store_info;
 ​
 select min(sales) from store_info;
 ​
 select max(sales) from store_info;
 ​
 select avg(sales) from store_info;
 ​
 select count(sales) from store_info;
 ​
 select concat('abc','123');
 ​
 select concat('abc',' ','123');
 ​
 ​
 select * from location;
 ​
 select * from store_info;
 ​
 select * from location where store_name='New York';
 ​
 ​
 select concat(Region,store_name) from location where store_name='New York';
 ​
 select concat(Region,'+',store_name) from location where store_name='New York';
 ​
 select region || store_name from location;
 ​
 select region || ' ' || store_name from location;
 ​
 select substr(store_name,5) from location where store_name='Los Angeles';
 ​
 select substr(store_name,5,6) from location where store_name='Los Angeles';
 ​
 select store_name, sum(sales) from store_info group by store_name order by sales desc;
 ​
 select store_name, sum(sales) from store_info group by store_name having sum(sales) > 1500;
 ​
 ​
 select a.store_name store, sum(a.sales) "total sales" from store_info a group by a.store_name;
 ​
 select sum(sales) from store_info where store_name in (select store_name from location where region = 'west');
 ​
 select sum(a.sales) from store_info a where a.store_name in (select store_name from location b where b.store_name = a.store_name);
 ​
 select sum(sales) from store_info where exists (select * from location where region = 'West');
 ​
 update store_info set store_name='Washington' WHERE sales=300;
 ​
 select * from store_info;
 ​
 ​
 select * from location a right join store_info b on a.store_name = b.store_name ;
 ​
 select * from location a left join store_info b on a.store_name = b.store_name ;
 ​
 ​
 select * from location a inner join store_info b on a.store_name = b.store_name ;
 ​
 select * from location a, store_info b where a.store_name = b.store_name;
 ​
 select a.region region, sum(b.sales) sales from location a, store_info b where a.store_name = b.store_name group by region;
 ​
 select store_name from location union select store_name from store_info;
 ​
 select store_name from location union all select store_name from store_info;
 ​
 select A.store_name from location A inner join store_info B ON A.store_name = B.store_ore_name;
 ​
 select A.store_name from location A inner join store_info B using(store_name);