oracle 使用 ALTER 操作列

 1 SQL> desc testtable;
 2 Name     Type         Nullable Default Comments 
 3 -------- ------------ -------- ------- -------- 
 4 EMPNO    NUMBER(4)    Y                         
 5 ENAME    VARCHAR2(10) Y                         
 6 JOB      VARCHAR2(9)  Y                         
 7 MGR      NUMBER(4)    Y                         
 8 HIREDATE DATE         Y                         
 9 SAL      NUMBER(7,2)  Y                         
10 COMM     NUMBER(7,2)  Y                         
11 DEPTNO   NUMBER(2)    Y                         
12 
13 SQL>--增加列
14 SQL> alter table testtable
15   2  add photo blob
16   3  ;
17 Table altered
18 
19 SQL> desc testtable;
20 Name     Type         Nullable Default Comments 
21 -------- ------------ -------- ------- -------- 
22 EMPNO    NUMBER(4)    Y                         
23 ENAME    VARCHAR2(10) Y                         
24 JOB      VARCHAR2(9)  Y                         
25 MGR      NUMBER(4)    Y                         
26 HIREDATE DATE         Y                         
27 SAL      NUMBER(7,2)  Y                         
28 COMM     NUMBER(7,2)  Y                         
29 DEPTNO   NUMBER(2)    Y                         
30 PHOTO    BLOB         Y                         
31 
32 SQL>--修改列类型
33 SQL> alter table testtable 
34   2  modify deptno number(3);
35 Table altered
36 
37 SQL> desc testtable;
38 Name     Type         Nullable Default Comments 
39 -------- ------------ -------- ------- -------- 
40 EMPNO    NUMBER(4)    Y                         
41 ENAME    VARCHAR2(10) Y                         
42 JOB      VARCHAR2(9)  Y                         
43 MGR      NUMBER(4)    Y                         
44 HIREDATE DATE         Y                         
45 SAL      NUMBER(7,2)  Y                         
46 COMM     NUMBER(7,2)  Y                         
47 DEPTNO   NUMBER(3)    Y                         
48 PHOTO    BLOB         Y                         
49 
50 SQL>--删除列
51 SQL> alter table testtable 
52   2  drop column photo;
53 Table altered
54 
55 SQL> desc testtable;
56 Name     Type         Nullable Default Comments 
57 -------- ------------ -------- ------- -------- 
58 EMPNO    NUMBER(4)    Y                         
59 ENAME    VARCHAR2(10) Y                         
60 JOB      VARCHAR2(9)  Y                         
61 MGR      NUMBER(4)    Y                         
62 HIREDATE DATE         Y                         
63 SAL      NUMBER(7,2)  Y                         
64 COMM     NUMBER(7,2)  Y                         
65 DEPTNO   NUMBER(3)    Y                         
66 
67 SQL>--修改列名
68 SQL> alter table testtable 
69   2  rename column 
70   3  deptno to dno;
71 Table altered
72 
73 SQL> desc testtable;
74 Name     Type         Nullable Default Comments 
75 -------- ------------ -------- ------- -------- 
76 EMPNO    NUMBER(4)    Y                         
77 ENAME    VARCHAR2(10) Y                         
78 JOB      VARCHAR2(9)  Y                         
79 MGR      NUMBER(4)    Y                         
80 HIREDATE DATE         Y                         
81 SAL      NUMBER(7,2)  Y                         
82 COMM     NUMBER(7,2)  Y                         
83 DNO      NUMBER(3)    Y