例題SQL語句詳解-資料庫基本操作2
阿新 • • 發佈：2018-12-09
1.4 表的操作
1.4.1 顯示所有表
語法：
show tables1.4.2 建立表
語法：
create table [if not exists] 表名(
欄位名 資料型別 [null|not null] [auto_increment] [primary key] [comment],
欄位名 資料型別 [default]…
)engine=儲存引擎單詞
null | not null 空|非空
default 預設值
auto_increment 自動增長
primary key 主鍵
comment 備註
engine 引擎 innodb myisam memory 引擎是決定資料儲存的方式 建立簡單的表
mysql> create database itcast;
Query OK, 1 row affected (0.00 sec)
mysql> use itcast;
Database changed
mysql> show tables;
Empty set (0.05 sec)
# 建立表
mysql> create table stu(
-> id int,
-> name varchar(30)
-> );
Query OK, 0 rows affected (0.13 sec)
# 檢視建立的表
mysql> show tables;
+------------------+ 建立複雜的表
mysql> set names gbk; # 設定字元編碼
Query OK, 0 rows affected (0.05 sec)
mysql> create table if not exists teacher(
-> id int auto_increment primary key comment '主鍵',
-> name varchar(20) not 多學一招：create table 資料庫名.表名，用於給指定的資料庫建立表
mysql> create table data.stu( #給data資料庫中建立stu表
-> id int,
-> name varchar(10));
Query OK, 0 rows affected (0.00 sec)1.4.3 顯示建立表的語句
語法：
show create table 表名顯示建立teacher表的語句
mysql> show create table teacher;
+---------+--------------------------------------------------------------------------
-------------------------------------------------------------------------------------
-------------------------------------------------------------------------------------
-------+
| Table | Create Table
|
+---------+--------------------------------------------------------------------------
-------------------------------------------------------------------------------------
-------------------------------------------------------------------------------------
-------+
| teacher | CREATE TABLE `teacher` (
`id` int(11) NOT NULL AUTO_INCREMENT COMMENT '主鍵',
`name` varchar(20) NOT NULL COMMENT '姓名',
`phone` varchar(20) DEFAULT NULL COMMENT '電話號碼',
`add` varchar(100) DEFAULT '地址不詳' COMMENT '地址',
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |將兩個欄位豎著排列 show create table 表名\G
mysql> show create table teacher\G;
*************************** 1. row ***************************
Table: teacher
Create Table: CREATE TABLE `teacher` (
`id` int(11) NOT NULL AUTO_INCREMENT COMMENT '主鍵',
`name` varchar(20) NOT NULL COMMENT '姓名',
`phone` varchar(20) DEFAULT NULL COMMENT '電話號碼',
`add` varchar(100) DEFAULT '地址不詳' COMMENT '地址',
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)
1.4.4 查看錶結構
語法：
desc[ribe] 表名檢視teacher表的結構
mysql> describe teacher;
+-------+--------------+------+-----+----------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+----------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(20) | NO | | NULL | |
| phone | varchar(20) | YES | | NULL | |
| add | varchar(100) | YES | | 地址不詳 | |
+-------+--------------+------+-----+----------+----------------+
4 rows in set (0.08 sec)
mysql> desc teacher;
+-------+--------------+------+-----+----------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+----------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(20) | NO | | NULL | |
| phone | varchar(20) | YES | | NULL | |
| add | varchar(100) | YES | | 地址不詳 | |
+-------+--------------+------+-----+----------+----------------+
4 rows in set (0.01 sec)1.4.5 刪除表
語法：
drop table [if exists] 表1，表2,… 刪除表
mysql> drop table stu;
Query OK, 0 rows affected (0.08 sec)如果刪除一個不存在的表就會報錯，刪除的時候可以判斷一下，存在就刪除。
mysql> drop table stu;
ERROR 1051 (42S02): Unknown table 'stu'
mysql> drop table if exists stu;
Query OK, 0 rows affected, 1 warning (0.00 sec)可以一次刪除多個表
mysql> drop table a1,a2;
Query OK, 0 rows affected (0.00 sec)1.4.6 修改表
語法：alter table 表名1、新增欄位：alter table 表名add [column] 欄位名 資料型別 [位置]
例題一：新增欄位
mysql> alter table teacher add age int;
Query OK, 0 rows affected (0.09 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc teacher;
+-------+--------------+------+-----+----------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+----------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(20) | NO | | NULL | |
| phone | varchar(20) | YES | | NULL | |
| add | varchar(100) | YES | | 地址不詳 | |
| age | int(11) | YES | | NULL | |
+-------+--------------+------+-----+----------+----------------+
5 rows in set (0.00 sec)例題二：在第一個位置上新增欄位
mysql> alter table teacher add email varchar(30) first;
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc teacher;
+-------+--------------+------+-----+----------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+----------+----------------+
| email | varchar(30) | YES | | NULL | |
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(20) | NO | | NULL | |
| phone | varchar(20) | YES | | NULL | |
| add | varchar(100) | YES | | 地址不詳 | |
| age | int(11) | YES | | NULL | |
+-------+--------------+------+-----+----------+----------------+例題三：在指定的欄位後新增欄位
mysql> alter table teacher add sex varchar(2) after name;
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc teacher;
+-------+--------------+------+-----+----------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+----------+----------------+
| email | varchar(30) | YES | | NULL | |
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(20) | NO | | NULL | |
| sex | varchar(2) | YES | | NULL | |
| phone | varchar(20) | YES | | NULL | |
| add | varchar(100) | YES | | 地址不詳 | |
| age | int(11) | YES | | NULL | |
+-------+--------------+------+-----+----------+----------------+
7 rows in set (0.00 sec)2、刪除欄位：alter table 表 drop [column] 欄位名
mysql> alter table teacher drop email;
Query OK, 0 rows affected (0.06 sec)
Records: 0 Duplicates: 0 Warnings: 03、修改欄位(改名改型別)：alter table 表 change [column] 原欄位名 新欄位名 資料型別 …
將欄位sex改為xingbie，資料型別為int
mysql> alter table teacher change sex xingbie int;
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 04、修改欄位（不改名）:alter table 表 modify 欄位名 欄位屬性…
將性別的資料型別改為varchar(2)
mysql> alter table teacher modify xingbie varchar(2);
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 05、修改引擎：alter table 表名 engine=引擎名
mysql> alter table teacher engine=myisam;
Query OK, 0 rows affected (0.05 sec)
Records: 0 Duplicates: 0 Warnings: 06、修改表名：alter table 表名 rename to 新表名
mysql> alter table teacher rename to stu;
Query OK, 0 rows affected (0.00 sec)
mysql> show tables;
+------------------+
| Tables_in_itcast |
+------------------+
| stu |
+------------------+
1 row in set (0.00 sec)1.4.7 複製表
語法一：create table 新表 select 欄位 from 舊錶特點：不能複製父表的主鍵，能夠複製父表的資料
mysql> create table stu1 select * from stu;
Query OK, 1 row affected (0.06 sec)
Records: 1 Duplicates: 0 Warnings: 0
mysql> select * from stu1; # 檢視資料複製到新表中
+----+------+------+-------+
| id | name | addr | score |
+----+------+------+-------+
| 1 | rose | 上海 | 88 |
+----+------+------+-------+
1 row in set (0.00 sec)
mysql> desc stu1; # 主鍵沒有複製
+-------+-------------+------+-----+----------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+----------+-------+
| id | int(11) | NO | | 0 | |
| name | varchar(20) | NO | | NULL | |
| addr | varchar(50) | YES | | 地址不詳 | |
| score | int(11) | YES | | NULL | |
+-------+-------------+------+-----+----------+-------+
4 rows in set (0.00 sec)語法二：create table 新表 like 舊錶特點：只能複製表結構，不能複製表資料
Query OK, 0 rows affected (0.00 sec)
mysql> select * from stu2; # 資料沒有複製
Empty set (0.01 sec)
mysql> desc stu2; # 主鍵複製了
+-------+-------------+------+-----+----------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+----------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(20) | NO | | NULL | |
| addr | varchar(50) | YES | | 地址不詳 | |
| score | int(11) | YES | | NULL | |
+-------+-------------+------+-----+----------+----------------+
4 rows in set (0.00 sec)