MySql的基操勿六

2018/12/6 星期四 19:34:07

authot by dabaine

數據庫注釋;

 -- 這就是注釋
/*.....*/ 這也是注釋

創建庫;

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

查看所有數據庫;

show databses;

查看數據庫結構:

show create database dabaine;

查看當前數據庫;

select database();

修改數據庫;

alter database dabaine [character set "gbk"];

刪除數據庫;

drop database [if exists] dabaine;

使用數據庫;

use database;

創建表;

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

刪除表;

drop table dabaine;

查看表結構;

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

查看表的全部信息;

desc dabaine;

修改表結構;

增加字段:
alter table dabaine add [column],add [column]......;
修改類型:
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 [約束條件];
刪除字段:
alter table dabaine drop [column]; 
重命名:
rename table table_name to new_table_name;

修改表內容;

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";    
刪除:
eg1:delete from dabaine where name = "cody";
eg2:truncate table dabaine; --把表摧毀,重新創建一張新表;

查詢順序;

select [distinct] *|field ... from dabaine
	where (不分組篩選)
	group by field
	having (分組后篩選)
	order by field
	limit 

查詢別名;

selct distinct id + 10 as id from dabaine;

執行順序;

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

聚合函數;

select name, sum(grade) from dabaine group by name;
ifnull(grade,0) --如果grade為空,則給它定為0;

外鍵約束;

創建主表:
create table class(
	id int(10) primary key auto_increment,
	name varchar(20),
	age int(5)
);
主表添加數據(多條):
insert into class(name,age) values
		("cody",18),
 		("solider",19),
 		("guan",21),
 		("lee",22),
 		("strong",28),
 		("pig",38);
創建子表:
create table student(
	id int(10) primary key auto_increment,
	name varchar(20),
	age int(5),
	teacher_id int(10), --綁定外鍵的字段要和主表中的字段類型保持一致;
	constraint dabaine --給外鍵命名大白訥
	foreign key (teacher_id) --給子表的屬性選擇外鍵綁定 
	references class(id) --映射主表的屬性(追隨主表的id字段)
);
子表添加數據:
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);
這時,主表和子表已經有關聯了,不可以隨便刪除主表的記錄;
增加外鍵:
alter table son_table_name add constraint cody
		foreign key(son_table_field)
		references primary_table(field);
刪除外鍵:
alter table son_table_name drop foreign key cody;

級聯刪除(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 --級聯刪除
);
	constraint cody foreign key (teacher_id) 
	references class(id) 
	on delete set null --主表刪除后,子表記錄設置為空值,且子表的字段屬性不能設置為not null;
	        on delete restrict --拒絕對主表進行更新刪除操作;
	on delete no action --類似於restrict

多表查詢;

笛卡爾積連接:
        A表中的全部數據m條 * B表中的全部數據n條;
連接查詢~內連接:
	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     |
			+---------+----+---------+
連接查詢~左外連接(左連接):
	left join
	select tableA.id,tableA.name,tableB.name from tableA 
			left join tableB on tableA.id = tableB.tableA_id
	--左連接以左表為主,select所選擇的字段,左表中的記錄會全部顯示,而右表會去匹配左表里的記錄,沒有的則顯示空值;
			+----+---------+---------+
			| id | name    | name    |
			+----+---------+---------+
			|  1 | cody    | cody    |
			|  2 | solider | solider |
			|  3 | guan    | guan    |
			|  4 | lee     | cody    |
			|  5 | strong  | strong  |
			|  6 | pig     | lee     |
			+----+---------+---------+
連接查詢~右外連接(右連接):
	right join
	類似左連接,以右表為主;
			+------+---------+---------+
			| 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;

查詢嵌套:
	select * from table_name where  field in (select field from table_name);
復制表:
	create table new_table(select * from old_table); --原表中的約束不會復制過來,需要重新添加
	selcet * from table_name where exists 
		(selcet field from table_name where....)
	--exists 后面的語句會返回一個布爾值,true則執行前面的select語句,
				flase 則返回空值;

索引;

	unique(唯一索引),fulltext(全局索引),spatial(空間索引),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[(長度)] [asc|desc]);
	eg2:alter table table_name 
		add [unique|fulltext|spatial] index|key index_name (字段名[(長度)] [asc|desc]);
刪除索引:
	drop index index_name on table_name;
	unique:唯一索引的字段不能重復;
	多列索引:給多個字段添加索引 (field1,field2...)

事務;

     start transaction; --開啟事務
 Rollback; --回滾事務(撤銷)
 Commit;  --提交事務;
 savepoint; 保留點,事務處理中的臨時占位符;

 savepoint name;
 rollback to svaepoint_name;

存儲過程;