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  • 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]
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  • 原文地址:https://www.cnblogs.com/IS2120/p/6745859.html
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