myslq基本語法(3)
一.多表連接
當需要的查詢的數據不是來自一張表，二十來自多張表時，就需要用到多表連接查詢
select t1.*,t2.teacher from it_student t1, it_subject t2 where t1.subject = t2.name;
mysql> select t1.*,t2.teacher from it_student t1, it_subject t2 where t1.subject = t2.name; +----+----------+------+-------+----------+---------+------------+ | id |name | age | sex | salary | subject | teacher | +----+----------+------+-------+----------+---------+------------+ | 1 | xianqian | 23 | woman | 19000.00 | test | wanglaoshi | | 2 | xiaoming | 26 | man | 15000.30 | python | lilaoshi | | 3 | laowang | 29 | man | 16000.50 | python |lilaoshi | | 4 | xiaolong | 27 | man | 28000.00 | python | lilaoshi | | 5 | laowen | 30 | man | 12000.00 | test | wanglaoshi | +----+----------+------+-------+----------+---------+------------+ 5 rows in set (0.00 sec)
註意：
1.設置數據庫別名，與列類似，
t1,t2 分別為it_student，it_subject表的別名
2.笛卡兒積：表1的行數 * 表2的行數
缺點：只能顯示匹配的行
表1 inner join 表2 on 條件
select t1.*,t2.teacher from it_student t1 inner join it_subject t2 on t1.subject = t2.name;
mysql> select t1.*,t2.teacher from it_student t1 inner join it_subject t2 on t1.subject = t2.name; +----+----------+------+-------+----------+---------+------------+ | id | name | age | sex | salary | subject | teacher | +----+----------+------+-------+----------+---------+------------+ | 1 | xianqian | 23 | woman | 19000.00 | test | wanglaoshi | | 2 | xiaoming | 26 | man | 15000.30 | python | lilaoshi | | 3 | laowang | 29 | man | 16000.50 | python | lilaoshi | | 4 | xiaolong | 27 | man | 28000.00 | python | lilaoshi | | 5 | laowen | 30 | man | 12000.00 | test | wanglaoshi | +----+----------+------+-------+----------+---------+------------+ 5 rows in set (0.00 sec)
4.外連接
左外連接(left join)：左表中的數據能夠全部顯示
select t1.*,t2.teacher from it_student t1 left join it_subject t2 on t1.subject = t2.name;
mysql> select t1.*,t2.teacher from it_student t1 left join it_subject t2 on t1.subject = t2.name; +----+----------+------+-------+----------+---------+------------+ | id | name | age | sex | salary | subject | teacher | +----+----------+------+-------+----------+---------+------------+ | 2 | xiaoming | 26 | man | 15000.30 | python | lilaoshi | | 3 | laowang | 29 | man | 16000.50 | python | lilaoshi | | 4 | xiaolong | 27 | man | 28000.00 | python | lilaoshi | | 1 | xianqian | 23 | woman | 19000.00 | test | wanglaoshi | | 5 | laowen | 30 | man | 12000.00 | test | wanglaoshi | | 6 | laotian | 27 | man | NULL | NULL | NULL | +----+----------+------+-------+----------+---------+------------+ 6 rows in set (0.00 sec)
右外連接(right join)：右表中的數據能夠全部顯示
select t1.*,t2.teacher from it_student t1 right join it_subject t2 on t1.subject = t2.name;
mysql> select t1.*,t2.teacher from it_student t1 right join it_subject t2 on t1.subject = t2.name; +------+----------+------+-------+----------+---------+------------+ | id | name | age | sex | salary | subject | teacher | +------+----------+------+-------+----------+---------+------------+ | 1 | xianqian | 23 | woman | 19000.00 | test | wanglaoshi | | 2 | xiaoming | 26 | man | 15000.30 | python | lilaoshi | | 3 | laowang | 29 | man | 16000.50 | python | lilaoshi | | 4 | xiaolong | 27 | man | 28000.00 | python | lilaoshi | | 5 | laowen | 30 | man | 12000.00 | test | wanglaoshi | | NULL | NULL | NULL | NULL | NULL | NULL | houlaoshi | +------+----------+------+-------+----------+---------+------------+ 6 rows in set (0.00 sec)
二.子查詢
就是查詢語句中嵌套右查詢語句
示例：
select * from it_student where salary=(select max(salary) from it_student);
mysql> select * from it_student where salary=(select max(salary) from it_student); +----+----------+------+------+----------+---------+ | id | name | age | sex | salary | subject | +----+----------+------+------+----------+---------+ | 4 | xiaolong | 27 | man | 28000.00 | python | +----+----------+------+------+----------+---------+ 1 row in set (0.00 sec)
select * from it_student where subject in (select name from it_subject where teacher = ‘lilaoshi‘);
mysql> select * from it_student where subject in (select name from it_subject where teacher = ‘lilaoshi‘); +----+----------+------+------+----------+---------+ | id | name | age | sex | salary | subject | +----+----------+------+------+----------+---------+ | 2 | xiaoming | 26 | man | 15000.30 | python | | 3 | laowang | 29 | man | 16000.50 | python | | 4 | xiaolong | 27 | man | 28000.00 | python | +----+----------+------+------+----------+---------+ 3 rows in set (0.00 sec)
三.事務
1.什麽是事務
就是一系列將要執行或正在執行的操作(sql語句)
2.事務安全，一種保護數據的安全機制，就是保證數據的完整性，一致性，事務執行前和執行後，數據是完整的
3.事務的特性(ACID)
(1)原子性(atomicity)
就是把事務中的一系列操作當作一個整體，要麽全部執行，要麽都不執行
(2)一致性(consistency)
數據從一個狀態轉到另一個狀態，保證每一個狀態數據的完整性
(3)隔離性(isolation)
當有多個事務同時進行時，能夠保證各個事務之間不會相互影響
(4)持久性(durability)
當事務提交後，就會永久保存在數據庫中
4.事務安全機制只在innodb引擎有效，myisam引擎註重查詢快
5.事務處理的步驟
(1)事務的啟動
start transaction;
(2)執行一系列SQL語句
update it_student set ...
update it_student set ...
(3)commit/rollback
提交或回滾，
commit後所有操作都會永久保存到數據庫中
rollback後(2)步驟中執行所有SQL語句都不會寫入數據庫中
事務處理示例：
mysql> select * from it_student where name=‘xianqian‘; +----+----------+------+-------+----------+---------+ | id | name | age | sex | salary | subject | +----+----------+------+-------+----------+---------+ | 1 | xianqian | 23 | woman | 19000.00 | test | +----+----------+------+-------+----------+---------+ 1 row in set (0.00 sec) mysql> start transaction; Query OK, 0 rows affected (0.00 sec) mysql> update it_student set salary=salary+5000 where name=‘xianqian‘; Query OK, 1 row affected (0.00 sec) Rows matched: 1 Changed: 1 Warnings: 0 mysql> select * from it_student where name=‘xianqian‘; +----+----------+------+-------+----------+---------+ | id | name | age | sex | salary | subject | +----+----------+------+-------+----------+---------+ | 1 | xianqian | 23 | woman | 24000.00 | test | +----+----------+------+-------+----------+---------+ 1 row in set (0.00 sec) mysql> rollback; Query OK, 0 rows affected (0.01 sec) mysql> select * from it_student where name=‘xianqian‘; +----+----------+------+-------+----------+---------+ | id | name | age | sex | salary | subject | +----+----------+------+-------+----------+---------+ | 1 | xianqian | 23 | woman | 19000.00 | test | +----+----------+------+-------+----------+---------+ 1 row in set (0.00 sec)
四.用戶管理
1.用戶創建
create user ‘用戶名‘@‘主機信息‘ identified by ‘123‘; # 本機可以使用localhost或127.0.0.1
create user ‘tom‘@‘localhost‘ identified by ‘123‘;
mysql> create user ‘tom‘@‘localhost‘ identified by ‘123‘; Query OK, 0 rows affected (0.00 sec)
create user ‘tom‘@‘192.168.211.103‘ identified by ‘123‘;
mysql> create user ‘tom‘@‘192.168.211.103‘ identified by ‘123‘; Query OK, 0 rows affected (0.00 sec)
mysql> select user,host from mysql.user; +------+------------------+ | user | host | +------+------------------+ | root | 127.0.0.1 | | root | 152.136.89.241 | | tom | 192.168.211.103 | | root | 192.168.39.22 | | root | 36.112.0.68 | | root | ::1 | | jack | localhost | | root | localhost | | tom | localhost | | root | vm\_0\_2\_centos | +------+------------------+ 10 rows in set (0.00 sec)
用戶的主機表現形式
‘user‘@‘localhost‘ 表示user只能在本地通過socket登錄數據庫
‘user‘@‘192.168.0.1‘ 表示user用戶只能在192.168.0.1登錄數據庫
‘user‘@‘192.168.0.0/24‘ 表示user用戶可以在該網絡任意的主機登錄數據庫
‘user‘@‘%‘ 表示user用戶可以在所有的機器上登錄數據庫
2.用戶賦權
(1)grant賦權
grant 權限1 [,權限2...] on 數據庫名.數據表名 to ‘用戶名‘@‘主機信息‘;
grant 權限(field1,field2...) on 數據庫名.數據表名 to ‘用戶名‘@‘主機信息‘;
grant select,update(age) on db_itheima.it_student to ‘tom‘@‘localhost‘;
grant all on *.* to ‘tom‘@‘192.168.211.103‘;
mysql> grant all on *.* to ‘tom‘@‘192.168.211.103‘; Query OK, 0 rows affected (0.00 sec)
賦權完成後建議刷新授權表:flush privileges;
查看權限
show grants; # 查看當前用戶的權限
show grants for ‘tom‘@‘localhost‘;
mysql> show grants for ‘tom‘@‘192.168.211.103‘; +---------------------------------------------------------------------------------------------------------------------------+ | Grants for tom@192.168.211.103 | +---------------------------------------------------------------------------------------------------------------------------+ | GRANT ALL PRIVILEGES ON *.* TO ‘tom‘@‘192.168.211.103‘ IDENTIFIED BY PASSWORD ‘*23AE809DDACAF96AF0FD78ED04B6A265E05AA257‘ | +---------------------------------------------------------------------------------------------------------------------------+ 1 row in set (0.00 sec)
註意：
a.*.* 代表所有數據庫的所有表
b.all 代表所有權限;usage 代表沒有權限，只有登錄數據庫,只可以使用test或test_*數據庫
c.grant賦權時加上 with grant option 可以讓被賦權的用戶有權限賦權給其他用戶，但是不能超過它本身具有的最大權限
示例：
grant all select,update,delete on db_itheima.* to ‘tom‘@‘localhost‘;
mysql -u tom -p登錄mysql
grant select ,update on db_itheima.* to ‘jack‘@‘loclahost‘; # jack的最大權限為select,update,delete on db_itheima.*
(2)創建用戶的同時賦權
grant select, update on db_itheima.* to ‘harry‘@‘localhost‘ identified by ‘1234‘;
mysql> grant select, update on db_itheima.* to ‘harry‘@‘localhost‘ identified by ‘1234‘; Query OK, 0 rows affected (0.00 sec) mysql> select user,host from mysql.user ; +-------+------------------+ | user | host | +-------+------------------+ | root | 127.0.0.1 | | root | 152.136.89.241 | | tom | 192.168.211.103 | | root | 192.168.39.22 | | root | 36.112.0.68 | | root | ::1 | | harry | localhost | | jack | localhost | | root | localhost | | tom | localhost | | root | vm\_0\_2\_centos | +-------+------------------+ 11 rows in set (0.00 sec)
(3)權限保存位置
mysql.user 所有mysql用戶的賬號和密碼，以及用戶對全庫全表權限（*.*）
mysql.db 非mysql庫的授權都保存在此(db.*)
mysql.table_priv 某庫某表的授權(db.table)
mysql.columns_priv 某庫某表某列的授權(db.table.col1)
mysql.procs_priv 某庫存儲過程的授權
3.收回權限
用戶有什麽權限就可以回收什麽權限
revoke select on db_itheima.* from ‘harry‘@‘localhost‘;
mysql> show grants for ‘harry‘@‘localhost‘ -> ; +--------------------------------------------------------------------------------------------------------------+ | Grants for harry@localhost | +--------------------------------------------------------------------------------------------------------------+ | GRANT USAGE ON *.* TO ‘harry‘@‘localhost‘ IDENTIFIED BY PASSWORD ‘*A4B6157319038724E3560894F7F932C8886EBFCF‘ | | GRANT SELECT, UPDATE ON `db_itheima`.* TO ‘harry‘@‘localhost‘ | +--------------------------------------------------------------------------------------------------------------+ 2 rows in set (0.00 sec) mysql> revoke select on db_itheima.* from ‘harry‘@‘localhost‘; Query OK, 0 rows affected (0.01 sec) mysql> show grants for ‘harry‘@‘localhost‘; +--------------------------------------------------------------------------------------------------------------+ | Grants for harry@localhost | +--------------------------------------------------------------------------------------------------------------+ | GRANT USAGE ON *.* TO ‘harry‘@‘localhost‘ IDENTIFIED BY PASSWORD ‘*A4B6157319038724E3560894F7F932C8886EBFCF‘ | | GRANT UPDATE ON `db_itheima`.* TO ‘harry‘@‘localhost‘ | +--------------------------------------------------------------------------------------------------------------+ 2 rows in set (0.00 sec)
4.刪除用戶
drop user ‘用戶名‘@‘主機信息‘;
drop user ‘tom‘@‘localhost‘;
delete from mysql.user where user=‘‘ and host=‘localhost‘ # 刪除本地匿名用戶
mysql> drop user ‘tom‘@‘localhost‘; Query OK, 0 rows affected (0.00 sec) mysql> select user,host from mysql.user where user=‘tom‘; +------+-----------------+ | user | host | +------+-----------------+ | tom | 192.168.211.103 | +------+-----------------+ 1 row in set (0.00 sec)
myslq基本語法(3)