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;
