Re: Deleting duplicate entries from MySQL database table

Manish wrote:
Sorry for not formulating the question properly.

The scenario is as:
1. A table is created
2. No Primary Key, Unique Key, Validation process.
3. Various duplicate entries gor inserted in the table (all fields
contain same data)

May be programming login bug.

In the edit process, nothing is edited, (all data are same), and
instead of updating the record, new row get inserted.

4. Now it is desired that all the entries with duplicate entries gets
deleted abd only 1 record (within duplicate entry) remains in the
table.

As in shown in example.

Suppose a table "address" contains the following records

-------------------------------------------------------
| name | address | phone |
-------------------------------------------------------
| mr x | 8th lane | 124364 |
| mr x | 6th lane | 435783 |
| mrs x | 6th lane | 435783 |
| mr x | 8th lane | 124364 |
-------------------------------------------------------

Execute single query (MySQL Version: No Restriction), with sub-query or some other method
After executing the query

-------------------------------------------------------
| name | address | phone |
-------------------------------------------------------
| mr x | 8th lane | 124364 |
| mr x | 6th lane | 435783 |
| mrs x | 6th lane | 435783 |
-------------------------------------------------------

Here instead of deleting both duplicate entry

| mr x | 8th lane | 124364 |

only one gets deleted (out of two) and no duplicate entries are there
in table.

Hope it will clarify my question.

Thanks.

Manish



Use distinct and create a new table.

INSERT INTO nodupes VALUES SELECT DISTINCT * FROM dupes

the distinct modifier will make sure all the rows of the result set are
different.

Note: this is under the assumption that all fields of the duplicate
rows are the same.

Another way is to create second table and set the primary key to
whatever should be unique part. Then do INSERT INTO IGNORE nodupes
VALUES SELECT * FROM dupes
The ignore portion will ignore any duplicate key errors.

Alvaro G. Vicario wrote:
*** Manish escribió/wrote (7 Jul 2006 04:11:54 -0700):
Please suggest on this

If you don't make a question I don't really what you kind of suggestions
you are expecting. Anyway, the best way to avoid duplicate information is
having a good design so the database is normalised and using primary keys
and unique indexes so the dupes cannot be physically inserted.


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.

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