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oracle菜鸟学习之 表操作
1.创建表
在oracle中，创建表使用create table来实现
SQL> create table student(sno number(6),sname varchar2(12),address varchar2(20));
Table created.
SQL> desc student;
Name Null? Type
----------------------------------------- -------- ----------------------------
SNO NUMBER(6)
SNAME VARCHAR2(12)
ADDRESS VARCHAR2(20)
SQL>
2.修改表的列
1.增加一列
SQL> alter table student add phone varchar(11);
Table altered.
SQL> desc student;
Name Null? Type
----------------------------------------- -------- ----------------------------
SNO NUMBER(6)
SNAME VARCHAR2(12)
ADDRESS VARCHAR2(20)
PHONE VARCHAR2(11)
SQL>
2.修改列属性,需要注意的是，如果修改的属性为长度，那么已存在的数据长度不能超过修改过后的数据长度。比如现存在一条信息，sname长度为6，如果你将sname的长度修改为5，那么将会出错。
# 这里使用到了modify（修改）
SQL> alter table student modify sname varchar2(5);
Table altered.
SQL> desc student;
Name Null? Type
----------------------------------------- -------- ----------------------------
SNO NUMBER(6)
SNAME VARCHAR2(5)
ADDRESS VARCHAR2(20)
PHONE VARCHAR2(11)
SQL>
```
### 3.删除列
在oracle中，删除列需要用column(列)
```
SQL> alter table student drop column phone;
Table altered.
SQL> desc student;
Name Null? Type
----------------------------------------- -------- ----------------------------
SNO NUMBER(6)
SNAME VARCHAR2(5)
ADDRESS VARCHAR2(20)
SQL>
3.插入数据
1.常规插入,所有的列都插入
SQL> insert into student values(1,'A','BJ');
1 row created.
SQL> select * from student;
SNO SNAME ADDRESS
---------- --------------- ------------------------------------
1 A BJ
2.插入空值
SQL> insert into student values(2,'B',null);
1 row created.
SQL> select * from student;
SNO SNAME ADDRESS
---------- --------------- ------------------------------------
1 A BJ
2 B
SQL>
3.指定列插入数据
SQL> insert into student(sno,address) values(3,'SH');
1 row created.
SQL> select * from student;
SNO SNAME ADDRESS
---------- --------------- ------------------------------------
1 A BJ
2 B
3 SH
SQL>
```
### 4.复制表
1.复制表的所有内容
```
SQL> create table student2 as select * from student;
Table created.
SQL> desc student2;
Name Null? Type
----------------------------------------- -------- ----------------------------
SNO NUMBER(6)
SNAME VARCHAR2(5)
ADDRESS VARCHAR2(12)
SQL> select * from student2;
SNO SNAME ADDRESS
---------- --------------- ------------------------------------
1 A BJ
2 B
3 SH
SQL>
```
2.只复制表结构，不复制内容
```
SQL> create table student3 as select * from student where 1>2;
Table created.
SQL> desc student3;
Name Null? Type
----------------------------------------- -------- ----------------------------
SNO NUMBER(6)
SNAME VARCHAR2(5)
ADDRESS VARCHAR2(12)
SQL> select * from student3;
no rows selected
SQL>
```
3.将student表的信息全部插入student3表中（也可以用where筛选）
```
SQL> select * from student3;
no rows selected
SQL> insert into student3 select * from student;
3 rows created.
SQL> select * from student3;
SNO SNAME ADDRESS
---------- --------------- ------------------------------------
1 A BJ
2 B
3 SH
SQL>
```
### 5.更新表
```
更新表中的内容
SQL> update student2 set sname='C' where sno=3;
1 row updated.
SQL> select * from student2;
SNO SNAME ADDRESS
---------- --------------- ------------------------------------
1 A BJ
2 B
3 C SH
SQL>
```
### 6.删除内容
1.删除某条信息,使用delete需要commit提交
```
SQL> delete student2 where sname='C';
1 row deleted.
SQL> select * from student2;
SNO SNAME ADDRESS
---------- --------------- ------------------------------------
1 A BJ
2 B
SQL> commit;
Commit complete.
```
2.清空表中的内容，保留表结构
使用delete的方式清除，需要提交，delete方式清除的内容会写入日志，可以恢复。
```
SQL> delete student3;
3 rows deleted.
SQL> select * from student3;
no rows selected
SQL> desc student3;
Name Null? Type
----------------------------------------- -------- ----------------------------
SNO NUMBER(6)
SNAME VARCHAR2(5)
ADDRESS VARCHAR2(12)
SQL> commit;
Commit complete.
```
3.使用truncate table 删除的内容不会写入日志，不可恢复，不需要提交
```
SQL> truncate table student2;
Table truncated.
SQL> select * from student2;
no rows selected
SQL> desc student2;
Name Null? Type
----------------------------------------- -------- ----------------------------
SNO NUMBER(6)
SNAME VARCHAR2(5)
ADDRESS VARCHAR2(12)
SQL>
```
### 7.删除表
```
SQL> drop table student3;
Table dropped.
SQL>
SQL>
SQL> desc student3;
ERROR:
ORA-04043: object student3 does not exist
```
### 8.重命名
```
1.表的重命名
格式：rename a to b;
SQL> rename student2 to newstudent;
Table renamed.
SQL> select * from newstudent;
SNO SNAME AGE
---------- ------------------------------ ----------
1 ZhangSan 21
2 FeiFei 22
3 WangWu 23
4 ZhaoYun 24
SQL>
2.重命名列
格式：alter table table_name rename column a to b;
SQL> alter table newstudent rename column age to sage;
Table altered.
SQL>
SQL> desc newstudent;
Name Null? Type
----------------------------------------- -------- ----------------------------
SNO NUMBER(6)
SNAME VARCHAR2(10)
SAGE NUMBER(38)
SQL>
```
### 9.查看所有表名
```
select * from tab;
```
完
