Swapping column values in Oracle

问题:

I was solving one of the puzzles and came across swapping column values using DML queries:

SELECT * FROM TEMP_TABLE;
ID1, ID2
--------
20, 15
20, 15
20, 15

Solution is mathematical calculation:

UPDATE TEMP_TABLE SET ID1=ID1+ID2;
UPDATE TEMP_TABLE SET ID2=ID1-ID2;
UPDATE TEMP_TABLE SET ID1=ID1-ID2;

Now, I am trying to figure out whether this can be applied to Strings or not, please suggest.

SELECT * FROM TEMP_TABLE_NEW;
ID1, ID2
--------
ABC, XYZ
ABC, XYZ
ABC, XYZ

回答1:

There's no need to have three update statements, one is sufficient:

UPDATE temp_table_new 
SET    id1 = id2, 
       id2 = id1; 

回答2:

CREATE TABLE Names
(
F_NAME VARCHAR(22),
L_NAME VARCHAR(22)
);

INSERT INTO Names VALUES('Ashutosh', 'Singh'),('Anshuman','Singh'),('Manu', 'Singh');

UPDATE Names N1 , Names N2 SET N1.F_NAME = N2.L_NAME , N1.L_NAME = N2.F_NAME 
WHERE N1.F_NAME = N2.F_NAME;

SELECT * FROM Names;

回答3:

Before:

select * from employ;

EMPNO FNAME      LNAME
----- ---------- ----------
 1001 kiran      kumar

 1002 santosh    reddy


update employ e set fname=(select lname from employ where empno=e.empno),
                    lname=(select fname from employ where empno=e.empno);

After:

 select * from employ;

 EMPNO FNAME      LNAME
------ ---------- ----------
  1001 kumar      kiran

  1002 reddy      santosh