oracle alter table详解

 

oracle alter table详解

//建测试表

1. create table dept(
2. deptno number(3) primary key,
3. dname varchar2(10),
4. loc varchar2(13)
5. );
6. create table employee_info(
7. empno number(3),
8. deptno number(3),
9. ename varchar2(10),
10. sex char(1),
11. phone number(11),
12. address varchar2(50),
13. introduce varchar2(100)
14. );
15. --
16. //0.重命名
17. //0.1 表:rename dept to dt;
18. rename dt to dept;
19. //0.2 列:alter table dept rename column loc to location;
20. alter table dept rename column location to loc;
21. //1.添加约束
22. //1.1 primary key
23. alter table employee_info add constraint pk_emp_info primary key(empno);
24. //1.2 foreign key
25. alter table employee_info add constraint fk_emp_info foreign key(deptno)
26. references dept(deptno);
27. //1.3 check
28. alter table employee_info add constraint ck_emp_info check
29. (sex in ('F','M'));
30. //1.4 not null
31. alter table employee_info modify phone constraint not_null_emp_info not null;
32. //1.5 unique
33. alter table employee_info add constraint uq_emp_info unique(phone);
34. //1.6 default
35. alter table employee_info modify sex char(2) default 'M';
36. //2.添加列
37. alter table employee_info add id varchar2(18);
38. alter table employee_info add hiredate date default sysdate not null;
39. //3.删除列
40. alter table employee_info drop column introduce;
41. //3.修改列
42. //3.1 修改列的长度
43. alter table dept modify loc varchar2(50);
44. //3.2 修改列的精度
45. alter table employee_info modify empno number(2);
46. //3.3 修改列的数据类型
47. alter table employee_info modify sex char(2);
48. //3.4 修改默认值
49. alter table employee_info modify hiredate default sysdate+1;
50. //4.禁用约束
51. alter table employee_info disable constraint uq_emp_info;
52. //5.启用约束
53. alter table employee_info enable constraint uq_emp_info;
54. //6.延迟约束
55. alter table employee_info drop constraint fk_emp_info;
56. alter table employee_info add constraint fk_emp_info foreign key(deptno)
57. references dept(deptno)
58. deferrable initially deferred;
59. //7.向表中添加注释
60. comment on table employee_info is 'information of employees';
61. //8.向列添加注释
62. comment on column employee_info.ename is 'the name of employees';
63. comment on column dept.dname is 'the name of department';
64. //9.清除表中所有数据
65. truncate table employee_info;
66. //10.删除表
67. drop table employee_info;
68. --
69. //下面来看看刚刚才我们对表dept和表employee_info所做的更改
70. //user_constraints视图里面包含了刚刚才我们创建的所有约束，以及其他信息，
71. //你可以用desc user_constraints命令查看其详细说明
72. select constraint_name,constraint_type,status,deferrable,deferred
73. from user_constraints
74. where table_name='EMPLOYEE_INFO';
75. --
76. CONSTRAINT_NAME CONSTRAINT_TYPE STATUS DEFERRABLE DEFERRED
77. ------------------------------ --------------- -------- -------------- ---------
78. PK_EMP_INFO P ENABLED NOT DEFERRABLE IMMEDIATE
79. FK_EMP_INFO R ENABLED DEFERRABLE DEFERRED
80. NOT_NULL_EMP_INFO C ENABLED NOT DEFERRABLE IMMEDIATE
81. SYS_C005373 C ENABLED NOT DEFERRABLE IMMEDIATE
82. UQ_EMP_INFO U ENABLED NOT DEFERRABLE IMMEDIATE
83. CK_EMP_INFO C ENABLED NOT DEFERRABLE IMMEDIATE
84. //我们可以通过user_cons_columns视图查看有关列的约束信息；
85. select owner,constraint_name,table_name,column_name
86. from user_cons_columns
87. where table_name='EMPLOYEE_INFO';
88. --
89. OWNER CONSTRAINT_NAME TABLE_NAME COLUMN_NAME
90. ------------------------------ ------------------------------ ------------------------------ ---------------
91. YEEXUN PK_EMP_INFO EMPLOYEE_INFO EMPNO
92. YEEXUN CK_EMP_INFO EMPLOYEE_INFO SEX
93. YEEXUN NOT_NULL_EMP_INFO EMPLOYEE_INFO PHONE
94. YEEXUN SYS_C005373 EMPLOYEE_INFO HIREDATE
95. YEEXUN UQ_EMP_INFO EMPLOYEE_INFO PHONE
96. YEEXUN FK_EMP_INFO EMPLOYEE_INFO DEPTNO
97. //我们将user_constraints视图与user_cons_columns视图连接起来
98. //查看约束都指向哪些列
99. column column_name format a15;
100. select ucc.column_name,ucc.constraint_name,uc.constraint_type,uc.status
101. from user_constraints uc,user_cons_columns ucc
102. where uc.table_name=ucc.table_name and
103. uc.constraint_name=ucc.constraint_name and
104. ucc.table_name='EMPLOYEE_INFO';
105. --
106. COLUMN_NAME CONSTRAINT_NAME CONSTRAINT_TYPE STATUS
107. --------------- ------------------------------ --------------- --------
108. EMPNO PK_EMP_INFO P ENABLED
109. DEPTNO FK_EMP_INFO R ENABLED
110. PHONE NOT_NULL_EMP_INFO C ENABLED
111. HIREDATE SYS_C005373 C ENABLED
112. PHONE UQ_EMP_INFO U ENABLED
113. SEX CK_EMP_INFO C ENABLED
114. --
115. //这里有个constraint_type，他具体指下面几种类型:
116. //C:check,not null
117. //P:primary key
118. //R:foreign key
119. //U:unique
120. //V:check option
121. //O:read only
122. --
123. //我们可以通过user_tab_comments视图获得对表的注释
124. select * from user_tab_comments
125. where table_name='EMPLOYEE_INFO';
126. TABLE_NAME TABLE_TYPE COMMENTS
127. ------------------------------ ----------- --------------------------
128. EMPLOYEE_INFO TABLE information of employees
129. --
130. //我们还可以通过user_col_comments视图获得对表列的注释：
131. select * from user_col_comments
132. where table_name='EMPLOYEE_INFO';
133. --
134. TABLE_NAME COLUMN_NAME COMMENTS
135. ------------------------------ ------------------------------ ---------------------------
136. EMPLOYEE_INFO EMPNO
137. EMPLOYEE_INFO DEPTNO
138. EMPLOYEE_INFO ENAME the name of employees
139. EMPLOYEE_INFO SEX
140. EMPLOYEE_INFO PHONE
141. EMPLOYEE_INFO ADDRESS
142. EMPLOYEE_INFO ID
143. EMPLOYEE_INFO HIREDATE
144. --
145. select * from user_col_comments
146. where table_name='EMPLOYEE_INFO' and
147. comments is not null;
148. --
149. TABLE_NAME COLUMN_NAME COMMENTS
150. ------------------------------ ------------------------------ ------------------------
151. EMPLOYEE_INFO ENAME the name of employees
152. --
153. //最后我们来查看一下修改后的表:
154. desc employee_info;
155. Name Type Nullable Default Comments
156. -------- ------------ -------- --------- ---------------------
157. EMPNO NUMBER(2)
158. DEPTNO NUMBER(3) Y
159. ENAME VARCHAR2(10) Y the name of employees
160. SEX CHAR(2) Y 'M'
161. PHONE NUMBER(11)
162. ADDRESS VARCHAR2(50) Y
163. ID VARCHAR2(18) Y
164. HIREDATE DATE sysdate+1
165. --
166. desc dept;
167. Name Type Nullable Default Comments
168. ------ ------------ -------- ------- ----------------------
169. DEPTNO NUMBER(3)
170. DNAME VARCHAR2(10) Y the name of department
171. LOC VARCHAR2(50) Y
172. --