MySql的基操勿六

2018/12/6 星期四 19:34:07

authot by dabaine

数据库注释;

 -- 这就是注释
/*.....*/ 这也是注释

创建库;

create databse [if not exists] dabaine [character set "utf8"];

查看所有数据库;

show databses;

查看数据库结构:

show create database dabaine;

查看当前数据库;

select database();

修改数据库;

alter database dabaine [character set "gbk"];

删除数据库;

drop database [if exists] dabaine;

使用数据库;

use database;

创建表;

create table dabaine(
	id smallint(10) primary key not null auto_increment,
	name varchar(25) not null,
    gender boolean not null
);

删除表;

drop table dabaine;

查看表结构;

eg1:show create table dabaine;
eg2:show columns from dabaine;

查看表的全部信息;

desc dabaine;

修改表结构;

增加字段:
alter table dabaine add [column],add [column]......;
修改类型:
alter table dabaine modify colum_name attribute [first|after column_name] colum_name;
修改列名:
alter table dabaine change column_name new_column_name type [约束条件];
删除字段:
alter table dabaine drop [column];
重命名:
rename table table_name to new_table_name;

修改表内容;

插入:
eg1:insert into dabaine (id, name) values(1,"dabaine");
eg2:insert into dabaine set id = 2,name="dabaine";
更新:
update dabaine set name="cody" where name="dabaine";
删除:
eg1:delete from dabaine where name = "cody";
eg2:truncate table dabaine; --把表摧毁,重新创建一张新表;

查询顺序;

select [distinct] *|field ... from dabaine
	where (不分组筛选)
	group by field
	having (分组后筛选)
	order by field
	limit

查询别名;

selct distinct id + 10 as id from dabaine;

执行顺序;

from,where,select,group by,having, order by

聚合函数;

select name, sum(grade) from dabaine group by name;
ifnull(grade,0) --如果grade为空,则给它定为0;

外键约束;

创建主表:
create table class(
	id int(10) primary key auto_increment,
	name varchar(20),
	age int(5)
);
主表添加数据(多条):
insert into class(name,age) values
		("cody",18),
 		("solider",19),
 		("guan",21),
 		("lee",22),
 		("strong",28),
 		("pig",38);
创建子表:
create table student(
	id int(10) primary key auto_increment,
	name varchar(20),
	age int(5),
	teacher_id int(10), --绑定外键的字段要和主表中的字段类型保持一致;
	constraint dabaine --给外键命名大白讷
	foreign key (teacher_id) --给子表的属性选择外键绑定
	references class(id) --映射主表的属性(追随主表的id字段)
);
子表添加数据:
insert into student(name,age,teacher_id) values
	("cody",18,1),
	("solider",19,2),
	("guan",21,3),
	("lee",22,4),
	("strong",28,5),
	("pig",38,6);
这时,主表和子表已经有关联了,不可以随便删除主表的记录;
增加外键:
alter table son_table_name add constraint cody
		foreign key(son_table_field)
		references primary_table(field);
删除外键:
alter table son_table_name drop foreign key cody;

级联删除(cascade);

create table studentNew(
	id int(10) primary key auto_increment,
	name varchar(20),
	age int(5),
	teacher_id int(10),
	constraint cody foreign key (teacher_id)
	references class(id)
	on delete cascade --级联删除
);
	constraint cody foreign key (teacher_id)
	references class(id)
	on delete set null --主表删除后,子表记录设置为空值,且子表的字段属性不能设置为not null;
	        on delete restrict --拒绝对主表进行更新删除操作;
	on delete no action --类似于restrict

多表查询;

笛卡尔积连接:
        A表中的全部数据m条 * B表中的全部数据n条;
连接查询~内连接:
	inner join
	eg1:select tableA.id,tableA.name,tableB.name from
			tableA,tableB where tableA.id = tableB.tableA_id
	eg2:select tableA.id,tableA.name,tableB.name from tableA
			inner join tableB on tableA.id = tableB.tableA_id
		   	+---------+----+---------+
			| name    | id | name    |
			+---------+----+---------+
			| cody    |  1 | cody    |
			| solider |  2 | solider |
			| guan    |  3 | guan    |
			| cody    |  4 | lee     |
			| strong  |  5 | strong  |
			| lee     |  6 | pig     |
			+---------+----+---------+
连接查询~左外连接(左连接):
	left join
	select tableA.id,tableA.name,tableB.name from tableA
			left join tableB on tableA.id = tableB.tableA_id
	--左连接以左表为主,select所选择的字段,左表中的记录会全部显示,而右表会去匹配左表里的记录,没有的则显示空值;
			+----+---------+---------+
			| id | name    | name    |
			+----+---------+---------+
			|  1 | cody    | cody    |
			|  2 | solider | solider |
			|  3 | guan    | guan    |
			|  4 | lee     | cody    |
			|  5 | strong  | strong  |
			|  6 | pig     | lee     |
			+----+---------+---------+
连接查询~右外连接(右连接):
	right join
	类似左连接,以右表为主;
			+------+---------+---------+
			| id   | name    | name    |
			+------+---------+---------+
			|    1 | cody    | cody    |
			|    4 | lee     | cody    |
			|    2 | solider | solider |
			|    3 | guan    | guan    |
			|    6 | pig     | lee     |
			|    5 | strong  | strong  |
			| NULL | NULL    | pig     |
			+------+---------+---------+

嵌套;

查询嵌套:
	select * from table_name where  field in (select field from table_name);
复制表:
	create table new_table(select * from old_table); --原表中的约束不会复制过来,需要重新添加
	selcet * from table_name where exists
		(selcet field from table_name where....)
	--exists 后面的语句会返回一个布尔值,true则执行前面的select语句,
				flase 则返回空值;

索引;

	unique(唯一索引),fulltext(全局索引),spatial(空间索引),index|key(普通索引)
添加索引:
	eg1:create
		[unique|fulltext|spatial] index|key
		index_name on table_name (字段名[(长度)] [asc|desc]);
	eg2:alter table table_name
		add [unique|fulltext|spatial] index|key index_name (字段名[(长度)] [asc|desc]);
删除索引:
	drop index index_name on table_name;
	unique:唯一索引的字段不能重复;
	多列索引:给多个字段添加索引 (field1,field2...)

事务;

     start transaction; --开启事务
 Rollback; --回滚事务(撤销)
 Commit;  --提交事务;
 savepoint; 保留点,事务处理中的临时占位符;
 savepoint name;
 rollback to svaepoint_name;

存储过程;