數據庫基礎二

時間  2019-11-13
標籤 數據庫 基礎 欄目 SQL 简体版
原文   原文鏈接

存儲引擎

  1. InnoDB 支持事務，外鍵，行級鎖
    事務：一個最小的不可再分的工做單元；一般一個事務對應一個完整的業務

 

事務四大特性：
1.原子性(A)：事務是最小單位，不可再分
2.一致性(C)：事務要求全部的DML語句操做的時候，   必須保證同時成功或者同時失敗
3.隔離性(I)：事務A和事務B之間具備隔離性
4.持久性(D)：是事務的保證，事務終結的標誌(內存的數據持久到硬盤文件中)

 

關於事務的一些術語
開啓事務：Start Transaction
事務結束：End Transaction
提交事務：Commit Transaction
回滾事務：Rollback Transaction

  1. MyIsam 表級鎖，支持全文索引
    只查詢多，修改少的時候使用
    myisam，同一張表中的數據不能被同時修改python

  2. memory 每一個用戶的登陸狀態
    數據都存在內存中，讀取速度快
    數據量小 並對服務器的內存有要求
    斷電消失mysql

  3. blackhole 黑洞
    放進去的全部數據都不存linux

 

sql語句

  1. 建立表

 

mysql> create table staff_info (id int,
       name varchar(20),
       age int,
       sex enum('female','male'),
       phone char(11),
       job varchar(20));
Query OK, 0 rows affected (0.20 sec)
  1. 查看錶結構
    mysql> desc staff_info;

 

+-------+-----------------------+------+-----+---------+-------+
| Field | Type                  | Null | Key | Default | Extra |
+-------+-----------------------+------+-----+---------+-------+
| id    | int(11)               | YES  |     | NULL    |       |
| name  | varchar(20)           | YES  |     | NULL    |       |
| age   | int(11)               | YES  |     | NULL    |       |
| sex   | enum('female','male') | YES  |     | NULL    |       |
| phone | char(11)              | YES  |     | NULL    |       |
| job   | varchar(20)           | YES  |     | NULL    |       |
+-------+-----------------------+------+-----+---------+-------+
  1. 插入數據

 

指定列名插入數據
mysql> insert into staff_info (id,name,age,sex,phone,job) values (1,'aa',83,'female','13651054608','IT');
Query OK, 1 row affected (0.02 sec)

插入單行數據
mysql> insert into staff_info values (2,'xm',82,'female','13651054608','IT');
Query OK, 1 row affected (0.02 sec)

插入多行數據
 mysql> insert into staff_info values
     -> (2,'ww',26,'male','13304320533','Tearcher'),
     -> (3,'ls',25,'male','13332353222','IT'),
     -> (4,'zs',40,'male','13332353333','IT');
  1. 查詢數據

 

# 查看全部列的數據
# mysql> select * from staff_info;
# +------+----------+------+--------+-------------+----------+
# | id   | name     | age  | sex    | phone       | job      |
# +------+----------+------+--------+-------------+----------+
# |    1 | xm     |   82 | female | 13651054608 | IT       |
# |    2 | ww     |   26 | male   | 13304320533 | Tearcher |
# |    3 | ls     |   25 | male   | 13332353222 | IT       |
# |    4 | zs     |   40 | male   | 13332353333 | IT       |
# +------+----------+------+--------+-------------+----------+
  1. 查看指定列的數據

 

# mysql> select name,age from staff_info;
# +----------+------+
# | name     | age  |
# +----------+------+
# | xm     |   82 |
# | ww     |   26 |
# | ls    |   25 |
# | zs |   40 |
# +----------+------+
# 4 rows in set (0.00 sec)

 

數據類型

經常使用
int
float
decimal
  1. 整數部分

 

# mysql> create table t5 (id1 int(4),id2 int);
# Query OK, 0 rows affected (0.16 sec)
#
# mysql> desc t5;
# +-------+---------+------+-----+---------+-------+
# | Field | Type    | Null | Key | Default | Extra |
# +-------+---------+------+-----+---------+-------+
# | id1   | int(4)  | YES  |     | NULL    |       |
# | id2   | int(11) | YES  |     | NULL    |       |
# +-------+---------+------+-----+---------+-------+
# 2 rows in set (0.01 sec)
#
# mysql> insert into t5 values (123,123);
# Query OK, 1 row affected (0.03 sec)
#
# mysql> select * from t5;
# +------+------+
# | id1  | id2  |
# +------+------+
# |  123 |  123 |
# +------+------+
# 1 row in set (0.00 sec)

# mysql> insert into t5 values (12345,12345);
# Query OK, 1 row affected (0.03 sec)
#
# mysql> select * from t5;
# +-------+-------+
# | id1   | id2   |
# +-------+-------+
# |   123 |   123 |
# | 12345 | 12345 |
# +-------+-------+
# 2 rows in set (0.00 sec)
#
# mysql> insert into t5 values (123,2147483648);
# Query OK, 1 row affected, 1 warning (0.02 sec)
#
# mysql> select * from t5;
# +-------+------------+
# | id1   | id2        |
# +-------+------------+
# |   123 |        123 |
# | 12345 |      12345 |
# |   123 | 2147483647 |
# +-------+------------+
# 3 rows in set (0.00 sec)

# 範圍測試 有符號和無符號
# mysql> create table t6 (id1 int(4),id2 int unsigned);
# Query OK, 0 rows affected (0.25 sec)
#
# mysql> insert into t6 values (123,2147483648);
# Query OK, 1 row affected (0.03 sec)
#
# mysql> select * from t6;
# +------+------------+
# | id1  | id2        |
# +------+------------+
# |  123 | 2147483648 |
# +------+------------+
# 1 row in set (0.00 sec)
  1. 小數

 

# 長度約束測試
# mysql> create table t7 (f float(10,3),d double(10,3),d2 decimal(10,3));
# Query OK, 0 rows affected (0.20 sec)
#
# mysql> insert into t7 values (1.23456789,2.34567,3.56789);
# Query OK, 1 row affected, 1 warning (0.02 sec)
#
# mysql> select * from t7;
# +-------+-------+-------+
# | f     | d     | d2    |
# +-------+-------+-------+
# | 1.235 | 2.346 | 3.568 |
# +-------+-------+-------+
# 1 row in set (0.00 sec)
  1. 精度測試

 

# mysql> create table t8 (f float(255,30),d double(255,30),d2 decimal(65,30));
# Query OK, 0 rows affected (0.18 sec)
# mysql> insert into t8 values (1.11111111111111111111111111111111111111111111111111111111111,1.11111111111111111111111111111111111111111111111111111111111,1.11111111111111111111111111111111111111111111111111111111111);
# Query OK, 1 row affected, 1 warning (0.02 sec)
# mysql> select * from t8;
# +----------------------------------+----------------------------------+----------------------------------+
# | f                                | d                                | d2                               |
# +----------------------------------+----------------------------------+----------------------------------+
# | 1.111111164093017600000000000000 | 1.111111111111111200000000000000 | 1.111111111111111111111111111111 |
# +----------------------------------+----------------------------------+----------------------------------+

 

時間類型

經常使用
date      描述年月日
datetime  描述年月日時分秒
  1. timestamp字段默認不爲空

 

# mysql> create table t9 (d date,t time,y year,dt datetime,ts timestamp);
# Query OK, 0 rows affected (0.18 sec)
#
# mysql> desc t9;
# +-------+-----------+------+-----+-------------------+-----------------------------+
# | Field | Type      | Null | Key | Default           | Extra                       |
# +-------+-----------+------+-----+-------------------+-----------------------------+
# | d     | date      | YES  |     | NULL              |                             |
# | t     | time      | YES  |     | NULL              |                             |
# | y     | year(4)   | YES  |     | NULL              |                             |
# | dt    | datetime  | YES  |     | NULL              |                             |
# | ts    | timestamp | NO   |     | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
# +-------+-----------+------+-----+-------------------+-----------------------------+
# 5 rows in set (0.01 sec)
#
# mysql> insert into t9 values (null,null,null,null,null);
# Query OK, 1 row affected (0.03 sec)
#
# mysql> select * from t9;
# +------+------+------+------+---------------------+
# | d    | t    | y    | dt   | ts                  |
# +------+------+------+------+---------------------+
# | NULL | NULL | NULL | NULL | 2018-09-29 11:27:29 |
# +------+------+------+------+---------------------+
# 1 row in set (0.00 sec)
#
# mysql> insert into t9 values(now(),now(),now(),now(),now());
# Query OK, 1 row affected, 1 warning (0.03 sec)
  1. 每種數據類型表示的時間格式

 

# mysql> select * from t9;
# +------------+----------+------+---------------------+---------------------+
# | d          | t        | y    | dt                  | ts                  |
# +------------+----------+------+---------------------+---------------------+
# | NULL       | NULL     | NULL | NULL                | 2018-09-29 11:27:29 |
# | 2018-09-29 | 11:29:07 | 2018 | 2018-09-29 11:29:07 | 2018-09-29 11:29:07 |
# +------------+----------+------+---------------------+---------------------+
# 2 rows in set (0.00 sec)
#
  1. datetime 和 timestamp的範圍控制

 

# mysql> insert into t9 (dt) values (10010101000000);
# Query OK, 1 row affected (0.03 sec)

# mysql> select * from t9;
# +------------+----------+------+---------------------+---------------------+
# | d          | t        | y    | dt                  | ts                  |
# +------------+----------+------+---------------------+---------------------+
# | NULL       | NULL     | NULL | NULL                | 2018-09-29 11:27:29 |
# | 2018-09-29 | 11:29:07 | 2018 | 2018-09-29 11:29:07 | 2018-09-29 11:29:07 |
# | NULL       | NULL     | NULL | 1001-01-01 00:00:00 | 2018-09-29 11:30:33 |
# +------------+----------+------+---------------------+---------------------+
# 3 rows in set (0.00 sec)

# mysql>
# mysql> insert into t9 (ts) values (10010101000000);
# Query OK, 1 row affected, 1 warning (0.03 sec)
#
# mysql> select * from t9;
# +------------+----------+------+---------------------+---------------------+
# | d          | t        | y    | dt                  | ts                  |
# +------------+----------+------+---------------------+---------------------+
# | NULL       | NULL     | NULL | NULL                | 2018-09-29 11:27:29 |
# | 2018-09-29 | 11:29:07 | 2018 | 2018-09-29 11:29:07 | 2018-09-29 11:29:07 |
# | NULL       | NULL     | NULL | 1001-01-01 00:00:00 | 2018-09-29 11:30:33 |
# | NULL       | NULL     | NULL | NULL                | 0000-00-00 00:00:00 |
# +------------+----------+------+---------------------+---------------------+
# 4 rows in set (0.00 sec)

 

字符串類型

CHAR	0-255字節	定長字符串
    # 定長 浪費磁盤 存取速度很是快
VARCHAR	0-65535 字節	變長字符串
    # 變長 節省磁盤空間 存取速度相對慢

char(5)     '  abc'  5   'abcde'  5
    # 這一列數據的長度變化小  手機號 身份證號 學號
    # 頻繁存取、對效率要求高
    # 短數據
varchar(5)  '3abc'   4   '5abcde' 6
    # 這一列的數據長度變化大  name  描述信息
    # 對效率要求相對小
    # 相對長

 

# mysql> create table t10 (c char(5),vc varchar(5));
# Query OK, 0 rows affected (0.14 sec)
#
# mysql> desc t10;
# +-------+------------+------+-----+---------+-------+
# | Field | Type       | Null | Key | Default | Extra |
# +-------+------------+------+-----+---------+-------+
# | c     | char(5)    | YES  |     | NULL    |       |
# | vc    | varchar(5) | YES  |     | NULL    |       |
# +-------+------------+------+-----+---------+-------+
# 2 rows in set (0.01 sec)

 

# 插入ab，實際上存儲中c佔用5個字節，vc只佔用3個字節，可是咱們查詢的額時候感知不到
# 由於char類型在查詢的時候會默認去掉全部補全的空格
# mysql> insert into t10 values ('ab','ab');
# Query OK, 1 row affected (0.03 sec)
#
# mysql> select * from t10;
# +------+------+
# | c    | vc   |
# +------+------+
# | ab   | ab   |
# +------+------+
# 1 row in set (0.00 sec)

 

# 插入的數據超過了約束的範圍，會截斷數據
# mysql> insert into t10 values ('abcdef','abcdef');
# Query OK, 1 row affected, 2 warnings (0.02 sec)
#
# mysql> select * from t10;
# +-------+-------+
# | c     | vc    |
# +-------+-------+
# | ab    | ab    |
# | abcde | abcde |
# +-------+-------+
# 2 rows in set (0.00 sec)

 

# 插入帶有空格的數據，查詢的時候能看到varchar字段是帶空格顯示的，char字段仍然在顯示的時候去掉了空格
# mysql> insert into t10 values ('ab    ','ab    ');
# Query OK, 1 row affected, 1 warning (0.03 sec)
#
# mysql> select * from t10;
# +-------+-------+
# | c     | vc    |
# +-------+-------+
# | ab    | ab    |
# | abcde | abcde |
# | ab    | ab    |
# +-------+-------+
# 3 rows in set (0.00 sec)
#
# mysql> select concat(c,'+'),concat(vc,'+') from t10;
# +---------------+----------------+
# | concat(c,'+') | concat(vc,'+') |
# +---------------+----------------+
# | ab+           | ab+            |
# | abcde+        | abcde+         |
# | ab+           | ab   +         |
# +---------------+----------------+
# 3 rows in set (0.01 sec)

 

枚舉和集合類型

枚舉 enum   單選
集合 set    多選

 

# mysql> create table t11 (name varchar(20),sex enum('male','female'),hobby set('抽菸','喝酒','燙頭','翻車'));
# Query OK, 0 rows affected (0.15 sec)
#
# mysql> desc t11;
# +-------+------------------------------------------+------+-----+---------+-------+
# | Field | Type                                     | Null | Key | Default | Extra |
# +-------+------------------------------------------+------+-----+---------+-------+
# | name  | varchar(20)                              | YES  |     | NULL    |       |
# | sex   | enum('male','female')                    | YES  |     | NULL    |       |
# | hobby | set('抽菸','喝酒','燙頭','翻車')         | YES  |     | NULL    |       |
# +-------+------------------------------------------+------+-----+---------+-------+
# 3 rows in set (0.01 sec)

 

# 若是插入的數據不在枚舉或者集合範圍內，數據沒法插入表
# mysql> insert into t11 values ('alex','aaaa','bbbb');
# Query OK, 1 row affected, 2 warnings (0.02 sec)
#
# mysql> select * from t11;
# +------+------+-------+
# | name | sex  | hobby |
# +------+------+-------+
# | alex |      |       |
# +------+------+-------+
# 1 row in set (0.00 sec)

 

# 向集合中插入數據，自動去重
# mysql> insert into t11 values ('alex','female','抽菸,抽菸,燙頭');
# Query OK, 1 row affected (0.03 sec)
#
# mysql> select * from t11;
# +------+--------+---------------+
# | name | sex    | hobby         |
# +------+--------+---------------+
# | alex |        |               |
# | alex | female | 抽菸,燙頭     |
# +------+--------+---------------+
# 2 rows in set (0.00 sec)

 

# 向集合中插入多條數據，不存在的項沒法插入
# mysql> insert into t11 values ('alex','female','抽菸,抽菸,燙頭,打豆豆');
# Query OK, 1 row affected, 1 warning (0.03 sec)
#
# mysql> select * from t11;
# +------+--------+---------------+
# | name | sex    | hobby         |
# +------+--------+---------------+
# | alex |        |               |
# | alex | female | 抽菸,燙頭     |
# | alex | female | 抽菸,燙頭     |
# +------+--------+---------------+
# 3 rows in set (0.00 sec)

 

完整性約束

not null      非空
unique        惟一 : 惟一能夠有一個空
惟一 + 非空
primary key   主鍵  惟一+非空 加速查詢 每張表只能有一個主鍵
foreign key   外鍵  Innodb

 

# primary key
    # 惟一+非空 每張表只能有一個主鍵
# not null      非空
# unique        惟一 : 惟一能夠有一個空

# not null + 惟一
    # 有一個能夠爲空了

 

# mysql> create table t12 (id int primary key,name varchar(20) not null,phone char(11) not null unique);
# Query OK, 0 rows affected (0.20 sec)
#
# mysql> desc t12;
# +-------+-------------+------+-----+---------+-------+
# | Field | Type        | Null | Key | Default | Extra |
# +-------+-------------+------+-----+---------+-------+
# | id    | int(11)     | NO   | PRI | NULL    |       |
# | name  | varchar(20) | NO   |     | NULL    |       |
# | phone | char(11)    | NO   | UNI | NULL    |       |
# +-------+-------------+------+-----+---------+-------+
# 3 rows in set (0.01 sec)
#
# mysql> insert into t12 (id,name) values (1,'alex');
# Query OK, 1 row affected, 1 warning (0.03 sec)
#
# mysql> select * from t12;
# +----+------+-------+
# | id | name | phone |
# +----+------+-------+
# |  1 | alex |       |
# +----+------+-------+
# 1 row in set (0.00 sec)
#
# mysql> insert into t12 (id,name) values (2,'egon');
# ERROR 1062 (23000): Duplicate entry '' for key 'phone'
# mysql> insert into t12 (id,name,phone) values (2,'egon','13434345678');
# Query OK, 1 row affected (0.03 sec)
#
# mysql> select * from t12;
# +----+------+-------------+
# | id | name | phone       |
# +----+------+-------------+
# |  1 | alex |             |
# |  2 | egon | 13434345678 |
# +----+------+-------------+
# 2 rows in set (0.00 sec)

 

# 不能輸入重複的值
# mysql> insert into t12 (name,phone) values ('egon','13434345678');
# ERROR 1062 (23000): Duplicate entry '13434345678' for key 'phone'
# mysql> insert into t12 (name,phone) values ('egon','13434345679');
# Query OK, 1 row affected, 1 warning (0.02 sec)

# mysql> select * from t12;
# +----+------+-------------+
# | id | name | phone       |
# +----+------+-------------+
# |  0 | egon | 13434345679 |
# |  1 | alex |             |
# |  2 | egon | 13434345678 |
# +----+------+-------------+
# 3 rows in set (0.00 sec)

 

# 主鍵也不能重複
# mysql> insert into t12 (name,phone) values ('egon','13434345677');
# ERROR 1062 (23000): Duplicate entry '0' for key 'PRIMARY'

 

# 建立部門表
# mysql> create table department (id int primary key auto_increment,dep_name varchar(20) not null);
# Query OK, 0 rows affected (0.16 sec)

# 建立員工表 外鍵關聯部門表中的id字段
# mysql> create table staff (sid int primary key auto_increment,sname varchar(20) not null,dep_id int, foreign key(dep_id) references department(id));
# Query OK, 0 rows affected (0.21 sec)

# mysql> desc staff;
# +--------+-------------+------+-----+---------+----------------+
# | Field  | Type        | Null | Key | Default | Extra          |
# +--------+-------------+------+-----+---------+----------------+
# | sid    | int(11)     | NO   | PRI | NULL    | auto_increment |
# | sname  | varchar(20) | NO   |     | NULL    |                |
# | dep_id | int(11)     | YES  | MUL | NULL    |                |
# +--------+-------------+------+-----+---------+----------------+
# 3 rows in set (0.01 sec)
#
# mysql> show create table staff;
# | Table | 
Create Table staff CREATE TABLE `staff` (
#   `sid` int(11) NOT NULL AUTO_INCREMENT,
#   `sname` varchar(20) NOT NULL,
#   `dep_id` int(11) DEFAULT NULL,
#   PRIMARY KEY (`sid`),
#   KEY `dep_id` (`dep_id`),
#   CONSTRAINT `staff_ibfk_1` FOREIGN KEY (`dep_id`) REFERENCES `department` (`id`)
# ) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
# 1 row in set (0.00 sec)

 

完整性約束補充

 

not null      非空
    # default 默認值
        # 若是不輸入就是用默認的實質
unique        惟一 : 惟一能夠有一個空
    # auto_increment  只有數字類型才能設置自增
    # 聯合惟一
        # 就是給一個以上的字段設置 惟一約束
primary key   主鍵  惟一+非空 加速查詢 每張表只能有一個主鍵
    # 當咱們以非空而且惟一的約束來建立一個表的時候，
    # 若是咱們沒有指定主鍵，那麼第一個非空惟一的字段將會被設置成主鍵
    # 聯合主鍵
        # 就是給一個以上的字段設置 惟一非空約束

foreign key   外鍵  Innodb
    # 外表中的一個惟一字段
    # on delete cascade
    # on update cascade

 

# course : cid,cname,cprice
# student : sid,sname,age,course_id

# 若是咱們沒有指定主鍵，那麼第一個非空惟一的字段將會被設置成主鍵
# mysql> create table t13 (id int unique not null);
# Query OK, 0 rows affected (0.15 sec)
#
# mysql> desc t13;
# +-------+---------+------+-----+---------+-------+
# | Field | Type    | Null | Key | Default | Extra |
# +-------+---------+------+-----+---------+-------+
# | id    | int(11) | NO   | PRI | NULL    |       |
# +-------+---------+------+-----+---------+-------+
# 1 row in set (0.01 sec)
#
# # 非空 + 惟一約束不能插入空值
# mysql> insert into t13 values (null);
# ERROR 1048 (23000): Column 'id' cannot be null
# mysql> create table t14 (id1 int unique not null,id2 int unique not null);
# Query OK, 0 rows affected (0.17 sec)
#
# mysql> desc t14;
# +-------+---------+------+-----+---------+-------+
# | Field | Type    | Null | Key | Default | Extra |
# +-------+---------+------+-----+---------+-------+
# | id1   | int(11) | NO   | PRI | NULL    |       |
# | id2   | int(11) | NO   | UNI | NULL    |       |
# +-------+---------+------+-----+---------+-------+
# 2 rows in set (0.01 sec)

 

# # 主鍵不能爲空值
# mysql> insert into t14 (id1) values (1);
# ERROR 1364 (HY000): Field 'id2' doesn't have a default value

 

# 指定主鍵以後 其餘的非空 + 惟一約束都不會再成爲主鍵
# mysql> create table t15 (id1 int unique not null,id2 int primary key);
# Query OK, 0 rows affected (0.23 sec)
#
# mysql> desc t15;
# +-------+---------+------+-----+---------+-------+
# | Field | Type    | Null | Key | Default | Extra |
# +-------+---------+------+-----+---------+-------+
# | id1   | int(11) | NO   | UNI | NULL    |       |
# | id2   | int(11) | NO   | PRI | NULL    |       |
# +-------+---------+------+-----+---------+-------+
# 2 rows in set (0.01 sec)
#
# mysql> insert into t15 values (1,2);
# Query OK, 1 row affected (0.03 sec)
#
# mysql> insert into t15 values (2,3);
# Query OK, 1 row affected (0.02 sec)
#
# mysql> insert into t15 values (4,4);
# Query OK, 1 row affected (0.03 sec)
#
# mysql> insert into t15 values (4,5);
# ERROR 1062 (23000): Duplicate entry '4' for key 'id1'
# mysql>

 

# 設置聯合主鍵
# mysql> create table t16 (id int,ip char(15),port int ,primary key(ip,port));
# Query OK, 0 rows affected (0.15 sec)
#
# mysql> desc t16;
# +-------+----------+------+-----+---------+-------+
# | Field | Type     | Null | Key | Default | Extra |
# +-------+----------+------+-----+---------+-------+
# | id    | int(11)  | YES  |     | NULL    |       |
# | ip    | char(15) | NO   | PRI |         |       |
# | port  | int(11)  | NO   | PRI | 0       |       |
# +-------+----------+------+-----+---------+-------+
# 3 rows in set (0.01 sec)
#
# mysql> insert into t16 values (1,'192.168.0.1','9000');
# Query OK, 1 row affected (0.02 sec)
#
# mysql> insert into t16 values (1,'192.168.0.1','9001');
# Query OK, 1 row affected (0.03 sec)
#
# mysql> insert into t16 values (1,'192.168.0.2','9000');
# Query OK, 1 row affected (0.03 sec)
#
# mysql> select * from t16
#     -> ;
# +------+-------------+------+
# | id   | ip          | port |
# +------+-------------+------+
# |    1 | 192.168.0.1 | 9000 |
# |    1 | 192.168.0.1 | 9001 |
# |    1 | 192.168.0.2 | 9000 |
# +------+-------------+------+
# 3 rows in set (0.00 sec)
#
# mysql> insert into t16 values (2,'192.168.0.2','9000');
# ERROR 1062 (23000): Duplicate entry '192.168.0.2-9000' for key 'PRIMARY'
# mysql>

 

# 設置ip和port兩個字段聯合惟一
# mysql> create table t17 (id int primary key,ip char(15) not null ,port int not null, unique(ip,port));
# Query OK, 0 rows affected (0.17 sec)
#
# mysql> desc t17;
# +-------+----------+------+-----+---------+-------+
# | Field | Type     | Null | Key | Default | Extra |
# +-------+----------+------+-----+---------+-------+
# | id    | int(11)  | NO   | PRI | NULL    |       |
# | ip    | char(15) | NO   | MUL | NULL    |       |
# | port  | int(11)  | NO   |     | NULL    |       |
# +-------+----------+------+-----+---------+-------+
# 3 rows in set (0.01 sec)
#
# mysql> insert into t17 values (1,'192.168.0.1',9000);
# Query OK, 1 row affected (0.03 sec)
#
# mysql> insert into t17 values (2,'192.168.0.1',9000);
# ERROR 1062 (23000): Duplicate entry '192.168.0.1-9000' for key 'ip'
# mysql> insert into t17 values (2,'192.168.0.1',9001);
# Query OK, 1 row affected (0.03 sec)
#
# mysql> insert into t17 values (3,'192.168.0.2',9001);
# Query OK, 1 row affected (0.03 sec)

 

# default 設置默認值
# mysql> create table t18 (id int primary key auto_increment,name varchar(20) not null,sex enum('male','female')
#     -> not null default 'male');
# Query OK, 0 rows affected (0.15 sec)
#
# mysql> desc t18;
# +-------+-----------------------+------+-----+---------+----------------+
# | Field | Type                  | Null | Key | Default | Extra          |
# +-------+-----------------------+------+-----+---------+----------------+
# | id    | int(11)               | NO   | PRI | NULL    | auto_increment |
# | name  | varchar(20)           | NO   |     | NULL    |                |
# | sex   | enum('male','female') | NO   |     | male    |                |
# +-------+-----------------------+------+-----+---------+----------------+
# 3 rows in set (0.01 sec)
#
# mysql> insert into t18 (name) values ('alex');
# Query OK, 1 row affected (0.03 sec)
#
# mysql> select * from t18;
# +----+------+------+
# | id | name | sex  |
# +----+------+------+
# |  1 | alex | male |
# +----+------+------+
# 1 row in set (0.00 sec)
#
# mysql> insert into t18 (name) values ('egon'),('yuan'),('nazha');
# Query OK, 3 rows affected (0.02 sec)
# Records: 3  Duplicates: 0  Warnings: 0
#
# mysql> select * from t18;
# +----+-------+------+
# | id | name  | sex  |
# +----+-------+------+
# |  1 | alex  | male |
# |  2 | egon  | male |
# |  3 | yuan  | male |
# |  4 | nazha | male |
# +----+-------+------+
# 4 rows in set (0.00 sec)
#
# mysql> insert into t18 (name,sex) values ('yanglan','female');
# Query OK, 1 row affected (0.03 sec)
#
# mysql> select * from t18;
# +----+---------+--------+
# | id | name    | sex    |
# +----+---------+--------+
# |  1 | alex    | male   |
# |  2 | egon    | male   |
# |  3 | yuan    | male   |
# |  4 | nazha   | male   |
# |  5 | yanglan | female |
# +----+---------+--------+
# 5 rows in set (0.00 sec)

 

# 外鍵 只有另外一個表中設置了unique的字段才能做爲本表的外鍵
# mysql> create table t20 (id int,age int,t19_id int,foreign key(t19_id) references t19(id));
# ERROR 1215 (HY000): Cannot add foreign key constraint
# mysql> create table t21 (id int unique ,name varchar(20));
# Query OK, 0 rows affected (0.17 sec)
#
# mysql> create table t20 (id int,age int,t_id int,foreign key(t_id) references t21(id));
# Query OK, 0 rows affected (0.21 sec)
#
# mysql> insert into t21 values (1,'python'),(2,'linux');
# Query OK, 2 rows affected (0.02 sec)

 

# 若是一個表找中的字段做爲外鍵對另外一個表提供服務，那麼默認不能直接刪除外表中正在使用的數據
# mysql> insert into t20 values (1,18,1);
# Query OK, 1 row affected (0.02 sec)
#
# mysql> insert into t20 values (2,38,2);
# Query OK, 1 row affected (0.02 sec)
#
# mysql> select * from t21;
# +------+--------+
# | id   | name   |
# +------+--------+
# |    1 | python |
# |    2 | linux  |
# +------+--------+
# 2 rows in set (0.00 sec)
#
# mysql> delete from t21 where id=1;
# ERROR 1451 (23000): Cannot delete or update a parent row: a foreign key constraint fails (`db2`.`t20`, CONSTRAINT `t20_ibfk_1` FOREIGN KEY (`t_id`) REFERENCES `t21` (`id`))

 

# 外鍵 on delete cascade on update cascade
# mysql> create table course (cid int primary key auto_increment,cname varchar(20) not null,
#     -> cprice int not null);
# Query OK, 0 rows affected (0.16 sec)
#
# mysql> create table student (sid int primary key auto_increment,
#     -> sname varchar(20) not null,
#     -> age int not null,
#     -> course_id int,
#     -> foreign key(course_id)
#     -> references course(cid)
#     -> on delete cascade
#     -> on update cascade);
# Query OK, 0 rows affected (0.17 sec)
#
# mysql> insert into course (cname,cprice) values ('python',19800),('linux',15800);
# Query OK, 2 rows affected (0.03 sec)
# Records: 2  Duplicates: 0  Warnings: 0
#
# mysql> insert into student (sname,age,course_id) values ('yangzonghe',18,1),('hesihao',88,2);
# Query OK, 2 rows affected (0.03 sec)
# Records: 2  Duplicates: 0  Warnings: 0
#
# mysql> delete from course where cid = 1;
# Query OK, 1 row affected (0.03 sec)
#
# mysql> select * from student;
# +-----+---------+-----+-----------+
# | sid | sname   | age | course_id |
# +-----+---------+-----+-----------+
# |   2 | hesihao |  88 |         2 |
# +-----+---------+-----+-----------+
# 1 row in set (0.00 sec)
#
# mysql> update course set cid = 1 where cid = 2;
# Query OK, 1 row affected (0.03 sec)
# Rows matched: 1  Changed: 1  Warnings: 0
#
# mysql> select * from course;
# +-----+-------+--------+
# | cid | cname | cprice |
# +-----+-------+--------+
# |   1 | linux |  15800 |
# +-----+-------+--------+
# 1 row in set (0.00 sec)
#
# mysql> select * from student;
# +-----+---------+-----+-----------+
# | sid | sname   | age | course_id |
# +-----+---------+-----+-----------+
# |   2 | hesihao |  88 |         1 |
# +-----+---------+-----+-----------+
# 1 row in set (0.00 sec)

 

表結構的修改

 

語法：
1. 修改表名
      ALTER TABLE 表名 
                      RENAME 新表名;

2. 增長字段
      ALTER TABLE 表名
                      ADD 字段名  數據類型 [完整性約束條件…],
                      ADD 字段名  數據類型 [完整性約束條件…];
                            
3. 刪除字段
      ALTER TABLE 表名 
                      DROP 字段名;

4. 修改字段
      ALTER TABLE 表名 
                      MODIFY  字段名 數據類型 [完整性約束條件…];
      ALTER TABLE 表名 
                      CHANGE 舊字段名 新字段名 舊數據類型 [完整性約束條件…];
      ALTER TABLE 表名 
                      CHANGE 舊字段名 新字段名 新數據類型 [完整性約束條件…];

5.修改字段排列順序/在增長的時候指定字段位置
    ALTER TABLE 表名
                     ADD 字段名  數據類型 [完整性約束條件…]  FIRST;
    ALTER TABLE 表名
                     ADD 字段名  數據類型 [完整性約束條件…]  AFTER 字段名;
    ALTER TABLE 表名
                     CHANGE 字段名  舊字段名 新字段名 新數據類型 [完整性約束條件…]  FIRST;
    ALTER TABLE 表名
                     MODIFY 字段名  數據類型 [完整性約束條件…]  AFTER 字段名;
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