Need help on How to delete duplicate data

Question

Hi All
I need your help in finding the best way to delete duplicate data from a table.
Table is like
create table table1 (col1 varchar2(10), col2 varchar2(20), col3 varchar2(30));
Insert into table1 ('ABC', 'DEF','FGH');
Insert into table1 ('ABC', 'DEF','FGH');
Insert into table1 ('ABC', 'DEF','FGH');
Insert into table1 ('ABC', 'DEF','FGH');
Now I want a sql statement which will delete the duplicate rows and leaves 1 row of that data in the table. ie.in the above example delete 3 rows of duplicate data and leave a row of that data in the table. My oracle version is 8i.
Appreciate your help in advance.

Answer 1

Either of these will work, the best approach will depend on how big the table is, and how many duplicates there are.
SQL> SELECT * FROM table1;
COL1       COL2                 COL3
ABC        DEF                  FGH
ABC        DEF                  FGH
ABC        DEF                  FGH
ABC        DEF                  FGH
ABC        DEF                  IJK
BCD        EFG                  HIJ
BCD        EFG                  HIJ
SQL> DELETE FROM table1 o
  2  WHERE rowid <> (SELECT MAX(rowid)
  3                  FROM table1 i
  4                  WHERE o.col1 = i.col1 and
  5                        o.col2 = i.col2 and
  6                        o.col3 = i.col3);
4 rows deleted.
SQL> SELECT * FROM table1;
COL1       COL2                 COL3
ABC        DEF                  FGH
ABC        DEF                  IJK
BCD        EFG                  HIJ
SQL> ROLLBACK;
Rollback complete.
SQL> CREATE TABLE table1_tmp AS
  2  SELECT DISTINCT * FROM table1;
Table created.
SQL> TRUNCATE TABLE table1;
Table truncated.
SQL> INSERT INTO table1
  2  SELECT * FROM table1_tmp;
3 rows created.
SQL> SELECT * FROM table1;
COL1       COL2                 COL3
ABC        DEF                  FGH
ABC        DEF                  IJK
BCD        EFG                  HIJThere are other approaches as well (e.g. see the EXCEPTIONS INTO clause of the ALTER TABLE command), but these are the most straightforward.
HTH
John