mysql學習筆記+MacOs

Mac安裝

安裝HomeBrew

/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

HomeBrew安裝MySql

#搜索版本
brew search mysql
#安裝MySQL
brew install [email protected]
#設置開機啓動
ln -sfv /usr/local/opt/[email protected]/*.plist ~/Library/LaunchAgents
#初始化操作，設置數據庫密碼，是否允許遠程登錄等等
mysql_secure_installation
#啓動數據庫
mysql.server start
#登錄
mysql -uroot -p
#關閉數據庫
mysql.server start
#可以查看提示來完成安裝運行
brew info [email protected]

error

#添加環境變量
echo 'export PATH="/usr/local/opt/[email protected]/bin:$PATH"' >> ~/.zshrc
source ~/.zshrc
#可以重啓一下數據庫
ERROR 1045 (28000): Access denied for user 'root'@'localhost'

---

MySQL使用

創建數據庫

create database niyadb;
show databases;
use niyadb;
drop database niyadb;

創建表

create table instructor;
show tables;
#查看錶的結構
mysql> desc instructor;
+-----------+-----------+------+-----+---------+-------+
| Field     | Type      | Null | Key | Default | Extra |
+-----------+-----------+------+-----+---------+-------+
| ID        | char(5)   | NO   |     | NULL    |       |
| name      | char(254) | NO   |     | NULL    |       |
| dept_name | char(254) | NO   |     | NULL    |       |
| salary    | int(11)   | NO   |     | NULL    |       |
+-----------+-----------+------+-----+---------+-------+
4 rows in set (0.01 sec)
#查看創建表的sql語句
show create table instructors;
#刪除表
drop table instructor;
#新增一列
alter table instructor 
add column birth 
varchar(256) 
not null;
#修改列
alter table instructor
change column birth new_name 
varchar(256)
not null;
#刪除列
alter table instructor
drop column birth;

插入行

insert into instructor values('10101','Srin','Comp','650');

查詢

基本查詢

#查詢所有數據
mysql> select  * from instructor;
+-------+--------+-----------+--------+
| ID    | name   | dept_name | salary |
+-------+--------+-----------+--------+
| 10101 | Srin   | Comp      |    650 |
| 12121 | Wu     | Finance   |    900 |
| 15151 | Mozart | Music     |    400 |
+-------+--------+-----------+--------+
3 rows in set (0.00 sec)
#測試數據庫連接
select 1;
+---+
| 1 |
+---+
| 1 |
+---+
1 row in set (0.00 sec)

按條件查詢

mysql> select * from instructor where salary>700;
+-------+------+-----------+--------+
| ID    | name | dept_name | salary |
+-------+------+-----------+--------+
| 12121 | Wu   | Finance   |    900 |
+-------+------+-----------+--------+
1 row in set (0.00 sec)

常用的條件表達式

=, >, >=, <, <= ,<>(不相等)，LIKE(相似)

mysql> select * from instructor where name like '%i%';
+-------+------+-----------+--------+
| ID    | name | dept_name | salary |
+-------+------+-----------+--------+
| 10101 | Srin | Comp      |    650 |
+-------+------+-----------+--------+
1 row in set (0.00 sec)

投影查詢

#可以指定輸出的列，可以修改列的順序
mysql> select name,id from instructor;
+--------+-------+
| name   | id    |
+--------+-------+
| Srin   | 10101 |
| Wu     | 12121 |
| Mozart | 15151 |
+--------+-------+
3 rows in set (0.00 sec)
#給name列起一個別名
mysql> select id,name new_name from instructor;
+-------+----------+
| id    | new_name |
+-------+----------+
| 10101 | Srin     |
| 12121 | Wu       |
| 15151 | Mozart   |
+-------+----------+
3 rows in set (0.00 sec)

排序

mysql> select * from instructor order by salary;
+-------+--------+-----------+--------+
| ID    | name   | dept_name | salary |
+-------+--------+-----------+--------+
| 15151 | Mozart | Music     |    400 |
| 10101 | Srin   | Comp      |    650 |
| 12121 | Wu     | Finance   |    900 |
+-------+--------+-----------+--------+
3 rows in set (0.00 sec)
#倒序輸出
mysql> select * from instructor order by salary DESC;
+-------+--------+-----------+--------+
| ID    | name   | dept_name | salary |
+-------+--------+-----------+--------+
| 12121 | Wu     | Finance   |    900 |
| 10101 | Srin   | Comp      |    650 |
| 15151 | Mozart | Music     |    400 |
+-------+--------+-----------+--------+
3 rows in set (0.00 sec)
#按多列排序,先按salary倒序排序，相同的行按dept_name排序
mysql> select * from instructor order by salary DESC,dept_name;
#帶where子句，order by要放在後面
mysql> select * from instructor where salary>600 order by salary DESC;
+-------+------+-----------+--------+
| ID    | name | dept_name | salary |
+-------+------+-----------+--------+
| 12121 | Wu   | Finance   |    900 |
| 10101 | Srin | Comp      |    650 |
| 17171 | Fang | History   |    650 |
+-------+------+-----------+--------+
3 rows in set (0.00 sec)

分頁查詢

#每頁3條記錄，從索引0開始取
mysql> select * from instructor
    -> order by salary
    -> limit 3 offset 0;
+-------+--------+-----------+--------+
| ID    | name   | dept_name | salary |
+-------+--------+-----------+--------+
| 15151 | Mozart | Music     |    400 |
| 10101 | Srin   | Comp      |    650 |
| 17171 | Fang   | History   |    650 |
+-------+--------+-----------+--------+
3 rows in set (0.00 sec)
#第2頁，從索引3開始取
mysql> select * from instructor order by salary limit 3 offset 3;
+-------+------+-----------+--------+
| ID    | name | dept_name | salary |
+-------+------+-----------+--------+
| 12121 | Wu   | Finance   |    900 |
+-------+------+-----------+--------+
1 row in set (0.00 sec)
#上面的語句可以簡寫成
mysql> select * from instructor order by salary limit 3, 3;

聚合查詢

#將查詢結果展示的列名設置別名count
mysql> select count(*) count from instructor;
+-------+
| count |
+-------+
|     4 |
+-------+
1 row in set (0.00 sec)
#可以使用where條件統計

聚合函數

SUM(only 數值), AVG（only 數值, MAX, MIN

mysql> select avg(salary) avg from instructor;
+----------+
| avg      |
+----------+
| 650.0000 |
+----------+
1 row in set (0.00 sec)
#也可以用條件子句where

分組聚合

#按salary分組並計數
mysql> select salary, count(*) count from instructor group by salary;
+--------+-------+
| salary | count |
+--------+-------+
|    400 |     1 |
|    650 |     2 |
|    900 |     1 |
+--------+-------+
3 rows in set (0.00 sec)

多表查詢

#給每個表設置一個簡單的別名，行兩兩拼在一起，列數相乘
mysql> select s.id,s.name,c.dept_name from instructor s,course c;
+-------+--------+-----------+
| id    | name   | dept_name |
+-------+--------+-----------+
| 10101 | Srin   | Finance   |
| 12121 | Wu     | Finance   |
| 15151 | Mozart | Finance   |
| 17171 | Fang   | Finance   |
| 10101 | Srin   | Finance   |
| 12121 | Wu     | Finance   |
| 15151 | Mozart | Finance   |
| 17171 | Fang   | Finance   |
| 10101 | Srin   | Finance   |
| 12121 | Wu     | Finance   |
| 15151 | Mozart | Finance   |
| 17171 | Fang   | Finance   |
| 10101 | Srin   | Comp      |
| 12121 | Wu     | Comp      |
| 15151 | Mozart | Comp      |
| 17171 | Fang   | Comp      |
| 10101 | Srin   | Music     |
| 12121 | Wu     | Music     |
| 15151 | Mozart | Music     |
| 17171 | Fang   | Music     |
+-------+--------+-----------+
20 rows in set (0.00 sec)
#後面同樣可以跟where子句

連接查詢

mysql> select * from instructor s 
mysql> inner join course c 
mysql> on s.dept_name=c.dept_name;
+-------+--------+-----------+--------+-----------+------------------+-----------+---------+
| ID    | name   | dept_name | salary | course_id | title            | dept_name | credits |
+-------+--------+-----------+--------+-----------+------------------+-----------+---------+
| 12121 | Wu     | Finance   |    900 | BOI-101   | Intro to Finance | Finance   |       4 |
| 12121 | Wu     | Finance   |    900 | BOI-301   | Genetics         | Finance   |       4 |
| 12121 | Wu     | Finance   |    900 | BOI-399   | Computional      | Finance   |       3 |
| 10101 | Srin   | Comp      |    650 | CS-101    | Game Design      | Comp      |       3 |
| 15151 | Mozart | Music     |    400 | MU-199    | World Music      | Music     |       3 |
+-------+--------+-----------+--------+-----------+------------------+-----------+---------+

inner join	內連接，交集
left outer join	左連接，左表爲基準，右表中不存在行填充NULL
right outer join	右連接，右表爲基準，左表中不存在行填充NULL
full outer join	全連接，並集

寫法：
1、確定主表from 表1；
2、需要連接的表 join 表2；
3、連接條件 on<條件……>；
4、可選添加子句。

修改數據

insert

#colume省略默認爲全部字段
#可以一次插入多條值，中間以逗號分隔
insert into tablename (colume1,colume2) 
values(value1,value2);

update

update tablename 
set colume1=value1,colume2=value2 
where colume=value;

delete

#刪除整行
delete from instructor;
#按條件刪除
delete from instructor where id=1;

退出

exit;

實用sql語句

#插入或者替換：查詢是否存在，存在-刪除+插入，不存在-插入
#使用replace可以查詢時刪除，而不是先查詢完再刪除
relpace into tablename values();
#插入或更新
insert into tablename
values()
on duplicate key update column1=value1,column2=value2;
#插入或忽略
insert ignore into tablename (column1,...) values(value1,...);
#快照
#複製一份當前表的數據到一個新表,想當於舊錶的查詢結果保存到了一個新的表裏
create table new_table select * from tablename where id=1;
#寫入查詢結果集
mysql> select * from new_instructor;
+-------+-----------+
| ID    | dept_name |
+-------+-----------+
| 10101 | Comp      |
| 12121 | Finance   |
| 17171 | History   |
+-------+-----------+
3 rows in set (0.00 sec)

mysql> insert into new_instructor (id,dept_name) select ID,dept_name from instructor;
Query OK, 4 rows affected (0.00 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql> select * from new_instructor;
+-------+-----------+
| ID    | dept_name |
+-------+-----------+
| 10101 | Comp      |
| 12121 | Finance   |
| 17171 | History   |
| 10101 | Comp      |
| 12121 | Finance   |
| 15151 | Music     |
| 17171 | History   |
+-------+-----------+
7 rows in set (0.00 sec)

事務 — 四種隔離級別

Read Uncommitted

問題：髒讀
一個事務可以獨當另一個事務更新但是未提交的數據，如果另一個事務回滾，那麼當前事務讀到的就是髒數據
讀不阻塞讀寫，寫阻塞寫不阻塞讀
行級鎖

Read Committed

問題：不可重複讀
一個事務多次讀取同一數據，如果中間有另一個事務修改了數據，那兩次讀的數據可能不一致
讀不阻塞讀寫，寫阻塞讀寫
行級鎖

Repeatable Read

問題：幻讀
讀記錄，記錄爲空，更新記錄時可以成功，再次讀有結果
讀阻塞寫不阻塞讀，寫阻塞讀寫
行級鎖

Serializable

最嚴格的的隔離級別
事務是串行執行（上面出現的三個問題都是因爲並行執行產生的），但是性能會急劇下降
默認隔離級別，MySQL中使用InnoDB默認隔離級別爲Repeatable Read
表級鎖

相關鎖

悲觀鎖

總是假設最壞的情況，每次去拿數據的時候都認爲別人會修改，所以每次在拿數據的時候都會上鎖，這樣別人想拿這個數據就會阻塞直到它拿到鎖（共享資源每次只給一個線程使用，其它線程阻塞，用完後再把資源轉讓給其它線程）。傳統的關係型數據庫裏邊就用到了很多這種鎖機制，比如行鎖，表鎖等，讀鎖，寫鎖等，都是在做操作之前先上鎖。

樂觀鎖

總是假設最好的情況，每次去拿數據的時候都認爲別人不會修改，所以不會上鎖，但是在更新的時候會判斷一下在此期間別人有沒有去更新這個數據，可以使用版本號機制和CAS算法實現。
樂觀鎖適用於多讀的應用類型，這樣可以提高吞吐量，像數據庫提供的類似於write_condition機制，其實都是提供的樂觀鎖。

行級鎖共享鎖

讀鎖，只讀不寫，之上可加讀鎖

行級鎖排它鎖

寫鎖，可讀可寫，不可加讀寫鎖

樂觀鎖之版本號與CAS算法

版本號機制

增加version字段，當前提交的version與數據庫當前version進行比較，大於即可提交，否則被駁回

CAS算法

compare and swap，無鎖算法，即不使用鎖的情況下實現多線程之間的變量同步，也叫非阻塞同步
需要讀寫的內存值V與A進行比較，加自旋鎖來更新V的值