如何为增加的列指定位置 (zz)

修改表的例子：

Examples

Add a column to a table
   ALTER TABLE STAFF_OPTIONS
      ADD SO_INSURANCE_PROVIDER Varchar2(35);

Add  a default value to a column
   ALTER TABLE STAFF_OPTIONS
      MODIFY SO_INSURANCE_PROVIDER Varchar2(35) DEFAULT 'ABC Ins';

Add two columns to a table and remove a constraint
   ALTER TABLE STAFF_OPTIONS
      ADD (SO_STAFF_ID INT, SO_PENSION_ID INT)
          STORAGE INITIAL 10 K
          NEXT 10 K
          MAXEXTENTS 121
          PCTINCREASE 0
          FREELISTS 2
      DROP CONSTRAINT cons_SO;

//z 2012-08-09 09:33:52 IS2120@csdn.T1428351245[T63,L414,R16,V609]
How does one add a column to the middle of a table?
Submitted by admin on Sat, 2005-12-03 00:53

Oracle only allows columns to be added to the end of an existing table. Example:

SQL> CREATE TABLE tab1 ( col1 NUMBER );

Table created.

//z 2012-08-09 09:33:52 IS2120@csdn.T1428351245[T63,L414,R16,V609]
SQL> ALTER TABLE tab1 ADD (col2 DATE);

Table altered.

SQL> DESC tab1
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 COL1                                               NUMBER
 COL2                                               DATE

Nevertheless, some databases also allow columns to be added to an existing table after a particular column (i.e. in the middle of the table). For example, in MySQL the following syntax is valid:

ALTER TABLE tablename ADD columnname AFTER columnname;

Oracle does not support this syntax. However, it doesn't mean that it cannot be done.

Workarounds:

1. Create a new table and copy the data across.

SQL> RENAME tab1 TO tab1_old;

Table renamed.

SQL> CREATE TABLE tab1 AS SELECT 0 AS col1, col1 AS col2 FROM tab1_old;

Table created.

2. Use the DBMS_REDEFINITION package to change the structure on-line while users are workining.
‹ Can one retrieve only the Nth row from a table? up How does one drop/ rename a columns in a table? ›
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How does one add a column to the middle of a table?
Submitted by samar bijaya panda (not verified) on Tue, 2006-02-21 06:21.

Here is another workaround:

create table emptest as select empno, 1 as id, 'x' as emp_name, ename from emp;

In the code above, replace 1 as id, 'x' as emp_name with your new columns.
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How does one add a column to the middle of a table?
Submitted by Kalyani P. Banerjee (not verified) on Tue, 2006-07-25 00:14.

To add a column in middle of the table of varchar data type:

SQL>create table test (ename varchar2(20),salary number);
Table created

SQL>desc test;
Name Null? Type
---------------------- ----------- ---------------
ENAME VARCHAR2(20) SALARY NUMBER

[i]SQL>rename test to test1;
Table renamed
[ii]SQL>create table test2 (id varchar2(20));
Table created
[iii]SQL>create table test as(select test1.ename,test2.id,test1.salary from test1,test2);
Table created
........................................................................................
SQL>desc test;
Name Null? Type
----------------------------------------- -------- --------------
ENAME VARCHAR2(20)
ID VARCHAR2(20)
SALARY NUMBER
»
//z 2012-08-09 09:33:52 IS2120@csdn.T1428351245[T63,L414,R16,V609]
How does one add a column to the middle of a table?
Submitted by SandhyaRR on Mon, 2010-09-27 03:09.

There is a table T with col1 and col2 and you want to add a new column col3 after col1.

1. Rename the column col2 to col3 as:
ALTER TABLE tablename RENAME COLUMN col2 TO col3;

2. Add a new column to the table
alter table t1 add (col2 datatype);

3.Now finally interchange the data contained in the two column:
UPDATE EMPLOYEE
SET col2 = col3
,col3 = col2

Note: Data types of the interchanged columns should match.
//z 2012-08-09 09:33:52 IS2120@csdn.T1428351245[T63,L414,R16,V609]