2018/12/6 星期四 19:34:07

authot by dabaine

資料庫註釋;

 -- 這就是註釋
/*.....*/ 這也是註釋

創建庫;

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

查看所有資料庫;

show databses;

查看資料庫結構:

show create database dabaine;

查看當前資料庫;

select database();

修改資料庫;

alter database dabaine [character set "gbk"];

刪除資料庫;

drop database [if exists] dabaine;

使用資料庫;

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;

增加欄位:
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];
刪除欄位:
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 (分組後篩選)
    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), --綁定外鍵的欄位要和主表中的欄位類型保持一致;
    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欄位)
);
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 --主表刪除後,子表記錄設置為空值,且子表的欄位屬性不能設置為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所選擇的欄位,左表中的記錄會全部顯示,而右表會去匹配左表裡的記錄,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);
複製表:
    create table new_table(select * from old_table); --原表中的約束不會複製過來,需要重新添加
    selcet * from table_name where exists 
        (selcet field from table_name where....)
    --exists 後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 (欄位名[(長度)] [asc|desc]);
    eg2:alter table table_name 
        add [unique|fulltext|spatial] index|key index_name (欄位名[(長度)] [asc|desc]);
刪除索引:
    drop index index_name on table_name;
    unique:唯一索引的欄位不能重覆;
    多列索引:給多個欄位添加索引 (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;