标签：include update insert style color
DML：Database Manipulate LanguageDML include:select,delete,insert into,update
aka == also known as
执行顺序
start --> [from --> [where] --> [[group by] --> [having]] --> [order by]] --> select --> [limit] --> end
select select_list from tb_name where condition;
select查询类型
1)简单查询，单表查询
2)多表查询
3)子查询，嵌套查询
所有 select * from tb_name;
选择 select * from tb_name where condition;
投影 select [distinct] field1,filed2,... from tb_name;
[distinct]去除重复选项
单表查询
- from子句，表示要查询的关系，表、多表、其他select语句
- where子句
逻辑关系操作符
条件判断操作符
>,<,=,<=>,between,in,like,rkike aka regexp，is null,is not null
<=> null safe euqal to;
example
mysql> select name,age,gender from students where not age>20 and not gender=‘M‘;
mysql> select name,age,gender from students where age between 20 and 25; 连续取值
mysql> select name,age from students where age in (19,25); 离散取值
mysql> select name from students where name like ‘L%‘;
mysql> select name from students where name like ‘Y____‘;
mysql> select name,age,gender from students where name rlike ‘^[YXN].*‘;
order by field_name [ASC|DESC]
mysql> select name,age from students order by age desc;
- limit [offset,]count子句，限制显示的行数
mysql> select name as student_name,age as age_number from students order by age desc limit 2,4;
mysql> select name as student_name,age as age_number from students order by age desc;
聚合：sum(),min(),max(),avg(),count()
having用于将group by的结果再次进行过滤
mysql> select cid1 as course,count(cid1) as total from students group by cid1;
mysql> select cid1 as course,count(cid1) as total from students group by cid1 having total>=2;
多表查询连接：
- 交叉连接：笛卡尔乘积，数据量大时不宜使用
- 自然连接
- 外连接
左外连接：... LEFT JOIN ... ON ...
右外连接: ... RIGHT JOIN ... ON ...
自然连接
mysql> select name,cname from students,courses where courses.cid=students.cid1;
mysql> select students.name,courses.cname from students,courses where courses.cid=students.cid1;标准写法
mysql> select s.name,c.cname from students as s,courses as c where c.cid=s.cid1; 表的别名
外连接
左外连接 mysql> select s.name,c.cname from students as s left join courses as c on c.cid=s.cid1;
右外连接 mysql> select s.name,c.cname from students as s right join courses as c on c.cid=s.cid1;
自连接
mysql> select s.name as student,t.name as teacher from students as s,students as t where t.sid=s.tid;
子查询1）比较操作中使用子查询：子查询只能返回单个值；
mysql> select name,age from students where age>(select avg(age) from students);
2）IN(): 使用子查询；
mysql> select name from students where age in (select age from tutors);
3）在FROM中使用子查询，可改写为多条件查询
联合查询UNION，只做联合不做判断mysql> (select name,age from students) union (select tname,age from tutors);
mysql> (select name,age from students) union (select tname,gender from tutors);
练习
1、挑选出courses表中没有被students中的CID2学习的课程的课程名称；
mysql> select cname from courses where cid not in (select distinct cid2 from students where cid2 is not null);
附加：挑选出没有教授任何课程的老师，每个老师及其所教授课程的对应关系在courses表中；
mysql> select tname from tutors where tutors.tid not in (select distinct courses.tid from courses );
找出students表中CID1有两个或两个以上同学学习了的同一个门课程的课程名称；
mysql> select cname from courses where courses.cid in (select cid1 from students group by cid1 having count(cid1)>=2);
2、显示每一位老师及其所教授的课程；没有教授的课程的保持为NULL；
mysql> select tname,cname from tutors left join courses on tutors.tid=courses.tid;
3、显示每一个课程及其相关的老师，没有老师教授的课程将其老师显示为空；
mysql> select tname,cname from tutors right join courses on tutors.tid=courses.tid;
4、显示每位同学CID1课程的课程名及其讲授了相关课程的老师的名称；
mysql> select name,cname,tname from students,courses,tutors where students.cid1=courses.cid and courses.tid=tutors.tid;
view 视图 虚表
基于基表的存储下来的select查询语句
创建视图
CREATE VIEW view_name AS select_statement
mysql> create view information as select name,cname,tname from students,courses,tutors where students.cid1=courses.cid and courses.tid=tutors.tid;
删除视图
DROP VIEW view_name
说明：
由于每次查看视图都要执行select语句，由于视图没有索引，性能可能没有多少提升；但是物化视图（mysql不支持），查询速度快；同时，视图可以用在只想让用户查看某些字段，增加安全性的情况。
insert
INSERT [LOW_PRIORITY | DELAYED | HIGH_PRIORITY] [IGNORE] [INTO] tbl_name [(col_name,...)] {VALUES | VALUE} ({expr | DEFAULT},...),(...),... [ ON DUPLICATE KEY UPDATE col_name=expr [, col_name=expr] ... ]
Or:一次插入一行指定字段的数据
INSERT [LOW_PRIORITY | DELAYED | HIGH_PRIORITY] [IGNORE] [INTO] tbl_name SET col_name={expr | DEFAULT}, ... [ ON DUPLICATE KEY UPDATE col_name=expr [, col_name=expr] ... ]
example
mysql> insert into students set name=‘Agan‘,age=26,gender=‘M‘,cid1=8,cid2 =7,tid=6,createtime=‘2016-05-26 18:01:30‘;
Or:将查询出来的数据加入表中
INSERT [LOW_PRIORITY | HIGH_PRIORITY] [IGNORE] [INTO] tbl_name [(col_name,...)] SELECT ...[ ON DUPLICATE KEY UPDATE col_name=expr[, col_name=expr] ... ]
mysql> insert into tutors (tname,gender,age) select name,gender,age from students where age > 10;
只显示最后插入的数据
mysql> select * from student order by sid desc limit 1,2;
mysql> select * from student order by sid desc limit 0,2;
显示计数器
mysql> select last_insert_id();
出现的问题:
使用 create table tb_name1 like tb_name2,若有auto_increment选项，则使用同一个计数器，两个表间的使用auto_increment字段的计数会累加
replace用法和insert类似
1）使用delete时，未使用where，可以禁止此操作；
2）计数器不变，在原来基础上继续计数
mysql> delete from student order by sid desc limit 10;
TRUNCATE [TABLE] tbl_name
清空表并清空auto_increment计数器
UPDATE tb_name SET col1=..., col2=... WHERE
SQL语句之DML
标签：include update insert style color
原文地址：http://hiyang.blog.51cto.com/10728919/1783594
