MySQL数据库的高级SQL语句！
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高级SQL语句
mysql进阶查询select
按关键字排序
- 使用order by语句来实现排序，排序可针对一个或多个字段
- ASC：升序（默认排序方式）
- DESC：降序
##order by 语法结构
select 字段1，字段2，字段3…… from 表名 where 条件表达式 order by 字段1，字段2 asc或desc;
查看某表的字段1，2，3，并根据字段1，2进行排序
mysql> select * from whd;
+------+-----------+------+
| id | name | age |
+------+-----------+------+
| 1 | zhangshan | 18 |
| 2 | lisi | 20 |
| 3 | wangwu | 25 |
| 4 | wangmazi | 22 |
| 5 | xuyi | 24 |
+------+-----------+------+
5 rows in set (0.00 sec)
mysql> select * from whd order by age asc;
##查看whd表，根据age字段进行升序排序，后面不加asc或者desc的话默认也为升序
+------+-----------+------+
| id | name | age |
+------+-----------+------+
| 1 | zhangshan | 18 |
| 2 | lisi | 20 |
| 4 | wangmazi | 22 |
| 5 | xuyi | 24 |
| 3 | wangwu | 25 |
+------+-----------+------+
5 rows in set (0.00 sec)
mysql> select * from whd where age>=22 order by age asc; #加入条件判断
+------+----------+------+
| id | name | age |
+------+----------+------+
| 4 | wangmazi | 22 |
| 5 | xuyi | 24 |
| 3 | wangwu | 25 |
+------+----------+------+
3 rows in set (0.00 sec)
or/and 或、且
mysql> select * from whd;
+------+-----------+------+-------+
| id | name | age | score |
+------+-----------+------+-------+
| 1 | zhangshan | 18 | 80 |
| 2 | lisi | 20 | 60 |
| 3 | wangwu | 25 | 60 |
| 4 | wangmazi | 22 | 90 |
| 5 | xuyi | 24 | 90 |
+------+-----------+------+-------+
5 rows in set (0.00 sec)
mysql> select * from whd where score >70 and score <=90;
+------+-----------+------+-------+
| id | name | age | score |
+------+-----------+------+-------+
| 1 | zhangshan | 18 | 80 |
| 4 | wangmazi | 22 | 90 |
| 5 | xuyi | 24 | 90 |
+------+-----------+------+-------+
3 rows in set (0.00 sec)
- 嵌套查询
mysql> select * from whd where id in (select id from test);
+------+-----------+------+-------+
| id | name | age | score |
+------+-----------+------+-------+
| 1 | zhangshan | 18 | 80 |
| 2 | lisi | 20 | 60 |
| 3 | wangwu | 25 | 60 |
+------+-----------+------+-------+
3 rows in set (0.00 sec)
mysql> select distinct score from whd; ##select后加distinct可以查看不重复的，即过滤重复的字段
+-------+，
| score |
+-------+
| 80 |
| 60 |
| 90 |
+-------+
3 rows in set (0.00 sec)
对结果进行分组
- group by 分组
select 字段名 from 表名 where 条件表达式 group by 字段名;
mysql> select count(name),age from whd group by score;
+-------------+------+
| count(name) | age |
+-------------+------+
| 2 | 20 |
| 1 | 18 |
| 2 | 22 |
+-------------+------+
- 现在结果条目查询
mysql> select * from whd order by score desc limit 2,4;
+------+-----------+------+-------+
| id | name | age | score |
+------+-----------+------+-------+
| 1 | zhangshan | 18 | 80 |
| 2 | lisi | 20 | 60 |
| 3 | wangwu | 25 | 60 |
+------+-----------+------+-------+
3 rows in set (0.00 sec
设置别名
在MySQL查询时，有的表名或字段名过长，为了方便书写或查询，可以对字段或表设置别名，增强可读性
select 字段名 as '别名' from 表名; #对字段设置别名
select 字段名 as '别名'，字段名2 as '别名' from 表名 as '别名';
mysql> select name as '姓名',age as '年龄' from whd;
+-----------+--------+
| 姓名 | 年龄 |
+-----------+--------+
| zhangshan | 18 |
| lisi | 20 |
| wangwu | 25 |
| wangmazi | 22 |
| xuyi | 24 |
+-----------+--------+
5 rows in set (0.00 sec)
mysql> create table text as select * from whd; #克隆表，不会复制主键
Query OK, 5 rows affected (0.01 sec)
Records: 5 Duplicates: 0 Warnings: 0
mysql> select * from text;
+------+-----------+------+-------+
| id | name | age | score |
+------+-----------+------+-------+
| 1 | zhangshan | 18 | 80 |
| 2 | lisi | 20 | 60 |
| 3 | wangwu | 25 | 60 |
| 4 | wangmazi | 22 | 90 |
| 5 | xuyi | 24 | 90 |
+------+-----------+------+-------+
5 rows in set (0.00 sec)
通配符
select * from 表名 where 条件表达式 like ‘字符串通配符’; #like表示模糊查询
- % :表示零个、一个或多个字符
- _ ：下划线表示单个字符
mysql> select * from whd where name like 'l_s_';
+------+------+------+-------+
| id | name | age | score |
+------+------+------+-------+
| 2 | lisi | 20 | 60 |
+------+------+------+-------+
1 row in set (0.00 sec)
mysql> select * from whd where name like 'w%';
+------+----------+------+-------+
| id | name | age | score |
+------+----------+------+-------+
| 3 | wangwu | 25 | 60 |
| 4 | wangmazi | 22 | 90 |
+------+----------+------+-------+
2 rows in set (0.00 sec)
子查询
子查询也叫内查询或者嵌套查询，指在一个查询语句中嵌套另一个查询语句，并且子查询语句是先于主语句被执行的，子查询的结果作为主查询的查询过滤
mysql> select id,name from whd where id in (select id from whd where score <80);
##如果是not in则表示取反
+------+--------+
| id | name |
+------+--------+
| 2 | lisi |
| 3 | wangwu |
+------+--------+
2 rows in set (0.00 sec)
- 子查询-exists：在子查询前面加exists是为了判断子查询结果是否成立，如果成立，则返回true值正常执行主语据的匹配，如果不成立则返回不成立，则不会执行主语据的查询
mysql> select id,name from whd where exists (select id from whd where score <80);
+------+-----------+
| id | name |
+------+-----------+
| 1 | zhangshan |
| 2 | lisi |
| 3 | wangwu |
| 4 | wangmazi |
| 5 | xuyi |
+------+-----------+
5 rows in set (0.00 sec)
mysql> select id,name from whd where exists (select id from whd where score >100);
Empty set (0.00 sec)
视图
数据库中的虚拟表，该表中不包含真是数据，只是做了映射，视图简化查询结果集、灵活查询、可以针对不同用户呈现不同结果集、有较高的安全性
##创建视图
create view 视图名 as select * from 表名 where 条件表达式
##创建多表视图
create view v_zuhe(id,name,score,age) as select test1.id,test1.name,test1.score,test2.age from test1,test2 where test1.name=test2.name;
mysql> create view v_socre as select * from whd where id>3;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from v_socre; #查看视图
+------+----------+------+-------+
| id | name | age | score |
+------+----------+------+-------+
| 4 | wangmazi | 22 | 90 |
| 5 | xuyi | 24 | 90 |
+------+----------+------+-------+
2 rows in set (0.01 sec)
mysql> update v_socre set age=18 where id=5;
##修改原表数据也会对视图产生影响,但是并不允许修改视图来修改原表，因为修改视图中的某些函数计算出的字段不会修改原表
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select * from whd;
+------+-----------+------+-------+
| id | name | age | score |
+------+-----------+------+-------+
| 1 | zhangshan | 18 | 80 |
| 2 | lisi | 20 | 60 |
| 3 | wangwu | 25 | 60 |
| 4 | wangmazi | 22 | 90 |
| 5 | xuyi | 18 | 90 |
+------+-----------+------+-------+
5 rows in set (0.00 sec)
- 视图和表的区别
（1）视图是已经编译好的sql语句，而表不是
（2）视图没有实际的物理记录，而表有
（3）表占有物理空间而表不占用物理空间
（4）视图时查看数据表的一种方法，只是一些SQL语句的集合
（5）视图的建立和删除只影响视图本身，不影响其对应的表
MySQL中的正则表达式
^ :匹配以什么字符为开头
$ :匹配以什么字符为结尾
. :表示任意单个字符
* :表示零个或多个字符
+ :表示前面的字符出现1次或多次
| :或
? :表示前面的字符零次或一次
[..] :匹配字符集合中的任意一个字符
[^..] :匹配不在括号中的内容
n :匹配前面字符串出现n次
n,m :匹配前面的字符串至少n次，最多m次
mysql> select id,name from whd where name regexp '^w';
+------+----------+
| id | name |
+------+----------+
| 3 | wangwu |
| 4 | wangmazi |
+------+----------+
2 rows in set (0.00 sec)
mysql> select id,name from whd where name regexp 'an|si';
+------+-----------+
| id | name |
+------+-----------+
| 1 | zhangshan |
| 2 | lisi |
| 3 | wangwu |
| 4 | wangmazi |
+------+-----------+
4 rows in set (0.00 sec)
mysql> select id,name from whd where name regexp '^[^w]'; #表示不匹配以W开头的
+------+-----------+
| id | name |
+------+-----------+
| 1 | zhangshan |
| 2 | lisi |
| 5 | xuyi |
+------+-----------+
3 rows in set (0.01 sec)
NULL值
数据库中NULL值表示缺少的值，表示在表中该字段是没有值的
null值和空值的区别： 空值长度为0，不占空间，NULL值的长度为null，占用空间，而当count（）计算时，NULL值会被忽略，而空值会加入计算
mysql> alter table whd add addr varchar(10); #添加一个字段
Query OK, 0 rows affected (0.04 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> select * from whd; #查看表内容
+------+-----------+------+-------+------+
| id | name | age | score | addr |
+------+-----------+------+-------+------+
| 1 | zhangshan | 18 | 80 | NULL |
| 2 | lisi | 20 | 60 | NULL |
| 3 | wangwu | 25 | 60 | NULL |
| 4 | wangmazi | 22 | 90 | NULL |
| 5 | xuyi | 18 | 90 | NULL |
+------+-----------+------+-------+------+
5 rows in set (0.00 sec)
mysql> update whd set addr='ai' where id>2; #修改表记录
Query OK, 3 rows affected (0.00 sec)
Rows matched: 3 Changed: 3 Warnings: 0
mysql> select * from whd; #查看修改结果
+------+-----------+------+-------+------+
| id | name | age | score | addr |
+------+-----------+------+-------+------+
| 1 | zhangshan | 18 | 80 | NULL |
| 2 | lisi | 20 | 60 | NULL |
| 3 | wangwu | 25 | 60 | ai |
| 4 | wangmazi | 22 | 90 | ai |
| 5 | xuyi | 18 | 90 | ai |
+------+-----------+------+-------+------+
5 rows in set (0.00 sec)
mysql> update whd set addr='' where id=2; #添加空值
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select * from whd;
+------+-----------+------+-------+------+
| id | name | age | score | addr |
+------+-----------+------+-------+------+
| 1 | zhangshan | 18 | 80 | NULL |
| 2 | lisi | 20 | 60 | |
| 3 | wangwu | 25 | 60 | ai |
| 4 | wangmazi | 22 | 90 | ai |
| 5 | xuyi | 18 | 90 | ai |
+------+-----------+------+-------+------+
5 rows in set (0.00 sec)
mysql> select count(addr) from whd; #计算addr字段的记录行数
+-------------+
| count(addr) |
+-------------+
| 4 |
+-------------+
1 row in set (0.00 sec)
mysql> update whd set addr='' where id=1; #将最后一个NULL值修改为空值
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select count(addr) from whd; #再次查看addr字段行数对比发现，空值会计算在内，而NULL在count（）计算中不会计算在内
+-------------+
| count(addr) |
+-------------+
| 5 |
+-------------+
1 row in set (0.00 sec)
算数运算
- 用select进行计算
mysql> select 1+2,2-1,3*2,4/2,5%2;
+-----+-----+-----+--------+------+
| 1+2 | 2-1 | 3*2 | 4/2 | 5%2 |
+-----+-----+-----+--------+------+
| 3 | 1 | 6 | 2.0000 | 1 |
+-----+-----+-----+--------+------+
1 row in set (0.00 sec)
mysql> create table ww as select 1+2,2-1,3*2,4/2,5%2; #创建一个表，将计算放入表中
Query OK, 1 row affected (0.00 sec)
Records: 1 Duplicates: 0 Warnings: 0
mysql> select * from ww;
+-----+-----+-----+--------+------+
| 1+2 | 2-1 | 3*2 | 4/2 | 5%2 |
+-----+-----+-----+--------+------+
| 3 | 1 | 6 | 2.0000 | 1 |
+-----+-----+-----+--------+------+
1 row in set (0.00 sec)
- 比较运算符
!=或<> :不等于
is null :判断是否给null
is not null :判断是否为非null
betweed and :两者之间
in :判断是否在集合中
like :通配符匹配
greatest :两个或多个参数时返回最大值
least :两个或多个参数时返回最小值
regexp :正则表达式
mysql> select 2=4,2=2,2='2','e'='e','r'=null; #等号判断值是否相等，结果0为错误，1为正确，如果结果有一个null，其结果就是null
+-----+-----+-------+---------+----------+
| 2=4 | 2=2 | 2='2' | 'e'='e' | 'r'=null |
+-----+-----+-------+---------+----------+
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