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Posted by anonieko on 06/13/00 11:40
> This is a common problem with some solution
>
>
/***********************************************************************************
*
* Problem:
* Determine the Duplicated Records in a table using single SELECT.
*
* We shall be using Northwind database, add some duplicate records.
*
* Here we want to know if 2 columns (CompanyName,
* PHone) are duplicated in a table.
*
*
* ShipperID CompanyName Phone
* ----------- ------------------------- ------------------
* 1 Speedy Express (503) 555-9831
* 2 United Package (503) 555-3199
* 3 Federal Shipping (503) 555-9931
* 4 Federal Shipping (503) 555-9931
* 5 Speedy Express (503) 555-9831
* 6 Federal Shipping (503) 555-9931
*
*
*
****************************************************/
==================================================
SOLUTION 1: Gives me the IDs that are duplicated.
==================================================
SELECT
ShipperID, CompanyName, Phone
FROM
SHIPPERS
WHERE
EXISTS (
SELECT
NULL
FROM
SHIPPERS b
WHERE
b.CompanyName = SHIPPERS.CompanyName
AND b.Phone = SHIPPERS.Phone
GROUP BY
b.CompanyName, b.Phone
HAVING
SHIPPERS.ShipperID < MAX( b.ShipperID )
)
/* ********************
* Output results
********************/
ShipperID CompanyName Phone
----------- ----------------------------------------
------------------------
1 Speedy Express (503) 555-9831
3 Federal Shipping (503) 555-9931
4 Federal Shipping (503) 555-9931
(3 row(s) affected)
=============================================================
SOLUTION 2: Gives me the data which are duplicate but
not the IDs
=============================================================
SELECT
CompanyName, Phone
FROM
SHIPPERS
GROUP BY
CompanyName, Phone
HAVING
COUNT(*) > 1
/* ********************
* Output results
********************/
CompanyName Phone
---------------------------------------- ------------------------
Speedy Express (503) 555-9831
Federal Shipping (503) 555-9931
(2 row(s) affected)
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