目录
- 高级查询
- select
- DISTINCT
- WHERE
- AND OR
- IN
- BETWEEN
- 通配符与like
- ORDER BY
- 数学函数
- 聚合函数
- 字符串函数
- mysql进阶查询
- GROUP BY
- HAVING
- 别名
- 子查询
- EXISTS
- 连接查询
- inner join(内连接)
- left join(左连接)
- right join(右连接)
- 自我连接
高级查询
实验准备：
第一张表：
create table location (Region char(20),Store_Name char(20));
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');
第二张表：
create table store_info (Store_Name char(20),Sales int(10),Date char(10));
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
---- SELECT ----显示表格中一个或数个字段的所有数据记录
语法：SELECT "字段" FROM "表名";
eg：
在store_info表中查找store_name的记录
select Store_Name from store_info;
+-------------+
| Store_Name |
+-------------+
| Los Angeles |
| Houston |
| Los Angeles |
| Boston |
+-------------+
在store_info表中查找store_name，sales,date的记录(字段顺序无所谓)
select store_name,sales,date from store_info;
+-------------+-------+------------+
| store_name | sales | date |
+-------------+-------+------------+
| Los Angeles | 1500 | 2020-12-05 |
| Houston | 250 | 2020-12-07 |
| Los Angeles | 300 | 2020-12-08 |
| Boston | 700 | 2020-12-08 |
+-------------+-------+------------+
DISTINCT
---- DISTINCT ----不显示重复的数据记录
语法：SELECT DISTINCT "字段" FROM "表名";
eg：
select distinct store_name from store_info;
+-------------+
| store_name |
+-------------+
| Los Angeles |
| Houston |
| Boston |
+-------------+
select distinct store_name,date from store_info;
+-------------+------------+
| store_name | date |
+-------------+------------+
| Los Angeles | 2020-12-05 |
| Houston | 2020-12-07 |
| Los Angeles | 2020-12-08 |
| Boston | 2020-12-08 |
+-------------+------------+
WHERE
---- WHERE ----有条件查询
语法：SELECT "字段" FROM "表名" WHERE "条件";
eg：
查找sales大于1000的store_name
select store_name from store_info where sales>1000;
+-------------+
| store_name |
+-------------+
| Los Angeles |
+-------------+
查找store_name为“Houston”的记录
select store_name,date,sales from store_info where store_name='Houston';
+------------+------------+-------+
| store_name | date | sales |
+------------+------------+-------+
| Houston | 2020-12-07 | 250 |
+------------+------------+-------+
AND OR
---- AND OR ----且 或
语法：SELECT "字段" FROM "表名" WHERE "条件1" {[AND|OR] "条件2"}+ ;
eg:
查找sales大于500且sales小于1000的store_name,sales,date
select store_name,sales,date from store_info where sales >500 and sales<1000;
+------------+-------+------------+
| store_name | sales | date |
+------------+-------+------------+
| Boston | 700 | 2020-12-08 |
+------------+-------+------------+
查找sales大于500且sales小于1000，或者sales大于1000的store_name,sales,date（注意把括号里的当成一个整体，并且优先执行）
select store_name,sales,date from store_info where (sales >500 and sales<1000) or sales > 1000;
+-------------+-------+------------+
| store_name | sales | date |
+-------------+-------+------------+
| Los Angeles | 1500 | 2020-12-05 |
| Boston | 700 | 2020-12-08 |
+-------------+-------+------------+
IN
---- IN ----显示已知的值的数据记录
语法：SELECT "字段" FROM "表名" WHERE "字段" IN ('值1', '值2', ...);
eg:
在store_info表中查找store_name为Los Angeles或者Houston的字段
select * from store_info where store_name in ('Los Angeles','Houston');
+-------------+-------+------------+
| Store_Name | Sales | Date |
+-------------+-------+------------+
| Los Angeles | 1500 | 2020-12-05 |
| Houston | 250 | 2020-12-07 |
| Los Angeles | 300 | 2020-12-08 |
+-------------+-------+------------+
在store_info表中查找store_name不为Los Angeles或者Houston的字段
select * from store_info where store_name not in ('Los Angeles','Houston');
+------------+-------+------------+
| Store_Name | Sales | Date |
+------------+-------+------------+
| Boston | 700 | 2020-12-08 |
+------------+-------+------------+
BETWEEN
---- BETWEEN ----显示两个值范围内的数据记录
语法：SELECT "字段" FROM "表名" WHERE "字段" BETWEEN '值1' AND '值2';
eg:
在store_info表中查找时间在2020-12-06到2020-12-11的数据
select * from store_info where date between '2020-12-06' and '2020-12-11';
通配符与like
---- 通配符 ----通常通配符都是跟 LIKE 一起使用的
% ：百分号表示零个、一个或多个字符
_ ：下划线表示单个字符
'A_Z'：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 'AKKZ' 并不符合 (因为在 A 和 Z 之间有两个字符，而不是一个字符)。
'ABC%': 所有以 'ABC' 起头的字符串。例如，'ABCD' 和 'ABCABC' 都符合这个模式。
'%XYZ': 所有以 'XYZ' 结尾的字符串。例如，'WXYZ' 和 'ZZXYZ' 都符合这个模式。
'%AN%': 所有含有 'AN'这个模式的字符串。例如，'LOS ANGELES' 和 'SAN FRANCISCO' 都符合这个模式。
'_AN%'：所有第二个字母为 'A' 和第三个字母为 'N' 的字符串。例如，'SAN FRANCISCO' 符合这个模式，而 'LOS ANGELES' 则不符合这个模式。
---- LIKE ----匹配一个模式来找出我们要的数据记录
语法：SELECT "字段" FROM "表名" WHERE "字段" LIKE {模式};
eg：
在store_info表中查找所有包含‘on’的数据
select * from store_info where store_name like '%on%';
ORDER BY
---- ORDER BY ----按关键字排序
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。
eg:
如果不指定排序方式，默认对sales字段进行升序排列
select * from store_info order by sales;
+-------------+-------+------------+
| Store_Name | Sales | Date |
+-------------+-------+------------+
| Houston | 250 | 2020-12-07 |
| Los Angeles | 300 | 2020-12-08 |
| Boston | 700 | 2020-12-08 |
| Los Angeles | 1500 | 2020-12-05 |
+-------------+-------+------------+
对sales字段进行降序排列
select * from store_info order by sales desc;
+-------------+-------+------------+
| Store_Name | Sales | Date |
+-------------+-------+------------+
| Los Angeles | 1500 | 2020-12-05 |
| Boston | 700 | 2020-12-08 |
| Los Angeles | 300 | 2020-12-08 |
| Houston | 250 | 2020-12-07 |
+-------------+-------+------------+
数学函数
eg：
select abs(-1),rand(),mod(5,3),power(2,3),round(1.89);
abs(-1）绝对值
rand（）生成 0 到 1 的随机数
mod(5,3) 5除以3的余数
power（2,3）2的3次方
round（1.89）1.89四舍五入后的结果
+---------+--------------------+----------+------------+-------------+
| abs(-1) | rand() | mod(5,3) | power(2,3) | round(1.89) |
+---------+--------------------+----------+------------+-------------+
| 1 | 0.4283285573388716 | 2 | 8 | 2 |
+---------+--------------------+----------+------------+-------------+
select round(1.8937,3),truncate(1.235,2),ceil(5.2),floor(2.1),least(1.89,3,6.1,2.1);
round(1.8937,3)四舍五入并保留三位小数
truncate(1.235,2)给1.235直接截断成2位小数
ceil(5.2)返回大于5.2的最小整数
floor(2.1)返回小于2.1的最大整数
least(1.89,3,6.1,2.1)返回这组数中最小的值
+-----------------+-------------------+-----------+------------+-----------------------+
| round(1.8937,3) | truncate(1.235,2) | ceil(5.2) | floor(2.1) | least(1.89,3,6.1,2.1) |
+-----------------+-------------------+-----------+------------+-----------------------+
| 1.894 | 1.23 | 6 | 2 | 1.89 |
+-----------------+-------------------+-----------+------------+-----------------------+
聚合函数
eg：
找到最大的sales
mysql> select max(sales) from store_info;
+------------+
| max(sales) |
+------------+
| 1500 |
+------------+
找到最小的sales
mysql> select min(sales) from store_info;
+------------+
| min(sales) |
+------------+
| 250 |
+------------+
求sales的平均值
mysql> select avg(sales) from store_info;
+------------+
| avg(sales) |
+------------+
| 687.5000 |
+------------+
求sales的和
mysql> select sum(sales) from store_info;
+------------+
| sum(sales) |
+------------+
| 2750 |
+------------+
新建一个city表，用来演示count()函数
create table city (name char(20));
insert into city values('nanjing');
insert into city values('hangzhou');
insert into city values('shanghai');
insert into city values();
insert into city values();
insert into city values('beijing');
insert into city values();
insert into city values();
select count(name) from city; #count（name）仅记录值不为NULL的
+-------------+
| count(name) |
+-------------+
| 4 |
+-------------+
select count(*) from city; #count（*）会将NULL值记录进去
+----------+
| count(*) |
+----------+
| 8 |
+----------+
字符串函数
返回去除指定格式的值
SELECT TRIM ([ [位置] [要移除的字符串] FROM ] 字符串);
#[位置]：的值可以为 LEADING (起头), TRAILING (结尾), BOTH (起头及结尾)。
#[要移除的字符串]：从字串的起头、结尾，或起头及结尾移除的字符串。缺省时为空格。
select trim(leading 'Ne' from 'New York');
将提供的参数 x 和 y 拼接成一个字符串
#将zhang和san拼接起来
select concat('zhang','san');
对location表中的两个字段进行合并，注意不要加引号
select concat(region,store_name) from location;
#如sql_mode开启了PIPES_AS_CONCAT，"||"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Concat相类似，这和Oracle数据库使用方法一样的
SELECT Region || ' ' || Store_Name FROM location WHERE Store_Name = 'Boston';
获取从字符串 x 中的第 y 个位置开始长度为 z 的字符串
#将region和store_name先进行拼接，并获取从第五个字符开始字符串
select substr(concat(region,store_name),5) from location;
#在store_name中从第五个字符开始，截取长度为6的字符串
select substr(store_name,5,6) from location where store_name='Los Angeles';
返回字符串 x 的长度
#返回store_name中，每个字段的的长度
select store_name,length(store_name) from location;
将字符串 z 替代字符串 x 中的字符串 y
#将st替换成stern
select replace(region,'st','stern') from location;
mysql进阶查询
GROUP BY
对GROUP BY后面的字段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，凡是在 GROUP BY 后面出现的字段，必须在 SELECT 后面出现；
凡是在 SELECT 后面出现的、且未在聚合函数中出现的字段，必须出现在 GROUP BY 后面
语法：SELECT "字段1", SUM("字段2") FROM "表名" GROUP BY "字段1";
#降序
select store_name,sum(sales) from store_info group by store_name order by sum(sales) desc;
#不指定默认升序
select store_name,sum(sales) from store_info group by store_name order by sum(sales);
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。
语法：SELECT "字段1", SUM("字段2") FROM "表格名" GROUP BY "字段1" HAVING (函数条件);
#eg:
select store_name,sum(sales) from store_info group by store_name having sum(sales)>1000;
别名
字段別名 表格別名
语法：SELECT "表格別名"."字段1" [AS] "字段別名" FROM "表格名" [AS] "表格別名";
#对字段设置别名
select store_name,sum(sales) as total from store_info group by store_name having sum(sales)>1000;
#对表设置别名
select store_name,sum(sales) from store_info as a group by a.store_name;
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：SELECT "字段1" FROM "表格1" WHERE "字段2" [比较运算符] #外查询
(SELECT "字段1" FROM "表格2" WHERE "条件"); #内查询
#可以是符号的运算符，例如 =、>、<、>=、<= ；也可以是文字的运算符，例如 LIKE、IN、BETWEEN
#括号里的查询语句作为where语句的查询条件
SELECT SUM(Sales) FROM store_info WHERE store_name IN (SELECT Store_Name FROM location WHERE Region = 'West');
EXISTS
用来测试内查询有没有产生任何结果，类似布尔值是否为真
#如果有的话，系统就会执行外查询中的SQL语句。若是没有的话，那整个 SQL 语句就不会产生任何结果。
语法：SELECT "字段1" FROM "表格1" WHERE EXISTS (SELECT * FROM "表格2" WHERE "条件");
SELECT SUM(Sales) FROM store_info WHERE EXISTS (SELECT * FROM location WHERE Region = 'West');
连接查询
inner join(内连接)：只返回两个表中联结字段相等的行
left join(左连接)：返回包括左表中的所有记录和右表中联结字段相等的记录
right join(右连接)：返回包括右表中的所有记录和左表中联结字段相等的记录
inner join(内连接)
#连接两个表中字段记录相等的数据记录
方法一：
select * from location A inner join store_info B on A.store_name=B.store_name;
方法二：
select * from location A, store_info B where A.store_name=B.store_name;
left join(左连接)
SELECT * FROM location A LEFT JOIN store_info B on A.Store_Name = B.Store_Name ;
right join(右连接)
SELECT * FROM location A RIGHT JOIN store_info B on A.Store_Name = B.Store_Name ;
自我连接
#分组汇总后统计 score 字段的值是比自己本身的值小的以及 score 字段 和 name 字段都相同的数量
select A.name,A.score,count(A.score) rank from student as A,student as B where A.score<=B.score group by A.name,A.score order by rank asc;
