Oracle 12c程序

Question

I have a table like,

Col1    Col2    Col3    Col4
1       abc      111    AAA
2       def      222    BBB
3       dhi      333    CCC

I need to change the column data using a stored procedure and the table should be like this,

Col1    Col2    Col3    Col4
AAA     111     abc      1
BBB     222     def      2
CCC     333     dhi      3


    col1 data should go to -> Col4
    col2 data should go to  -> Col3
    col3  data should go to -> Col2
    col4  data should go to -> Col1

Answer 1

The procedure will need to run this update statement:

CREATE PROCEDURE switch_cols IS
BEGIN
  UPDATE t
  SET col4 = col1,
      col3 = col2,
      col2 = col3,
      col1 = col4;
END;
/

Of course, this is assuming all columns are of the same type.

Answer 2

You need actualy to echnage the content of the column col1 and col4 respective the columns col2 and col3 . You need not to do any DML to achieve this, simple RENAME COLUMN is enough.

select Col1, Col2, Col3, Col4 from tab;

      COL1 COL2             COL3 COL4     
---------- ---------- ---------- ----------
         1 abc               111 AAA        
         2 def               222 BBB 


--- exchange col1 <-> col4
alter table TAB rename column col1 TO tmp;
alter table TAB rename column col4 TO col1;
alter table TAB rename column tmp TO col4;
--- exchange col2 <-> col3
alter table TAB rename column col2 TO tmp;
alter table TAB rename column col3 TO col2;
alter table TAB rename column tmp TO col3;

select Col1, Col2, Col3, Col4 from tab; 

COL1             COL2 COL3             COL4
---------- ---------- ---------- ----------
AAA               111 abc                 1 
BBB               222 def                 2 
CCC               333 dhi                 3  

This works even with different column types .

Example of the table before rename:

create table tab
(Col1 number,
Col2  varchar2(10),
Col3  number,
Col4  varchar2(10));

and after

CREATE TABLE  TAB 
("COL4" NUMBER, 
"COL3" VARCHAR2(10), 
"COL2" NUMBER, 
"COL1" VARCHAR2(10)
);

The big advantage of this approach is, that it is only metadate update, no real data update, so it is ready in instant time even for large tables. The only thing you must consider is, that you can't simple rename col1 to col4 if the table contains the colum col4 already. So you must rename the first column to a temporary name to get the target name free.

The only side effect is, that the order of theh columns in the table is different. If this is relevant, simple re-create the table with new name and finally rename the original table to backup and the new table to the productive name:

create table tab_new as
select 
col4 col1,
col3 col2,
col2 col3,
col1 col4
from tab;

rename tab to backup;
rename tab_new to tab;

You'll have to transfer existing indexes, constraints, triggers etc.