sql query to delete only one duplicate row - sql-server

Question

I've a table with some duplicate rows in it. I want to delete only one duplicate row.
For example I'v 9 duplicate rows so should delete only one row and should show 8 remaining rows.
example
date calling called duration timestampp
2012-06-19 10:22:45.000 165 218 155 1.9 121
2012-06-19 10:22:45.000 165 218 155 1.9 121
2012-06-19 10:22:45.000 165 218 155 1.9 121
2012-06-19 10:22:45.000 165 218 155 1.9 121
from above date should delete only one row and should show 3 rows
2012-06-19 10:22:45.000 165 218 155 1.9 100
2012-06-19 10:22:45.000 165 218 155 1.9 100
2012-06-19 10:22:45.000 165 218 155 1.9 100
from above date should delete only one row and should show 2 rows
How can I do this?

Answer 1

This solution allows you to delete one row from each set of duplicates (rather than just handling a single block of duplicates at a time):
;WITH x AS
(
SELECT [date], rn = ROW_NUMBER() OVER (PARTITION BY
[date], calling, called, duration, [timestamp]
ORDER BY [date])
FROM dbo.UnspecifiedTableName
)
DELETE x WHERE rn = 2;
As an aside, both [date] and [timestamp] are terrible choices for column names...

Answer 2

For SQL Server 2005+ you can do the following:
;WITH CTE AS
(
SELECT *,
ROW_NUMBER() OVER(PARTITION BY [date], calling, called, duration, [timestamp] ORDER BY 1) RN
FROM YourTable
)
DELETE FROM CTE
WHERE RN = 2

Answer 3

Do you have a primary key on the table?
What makes a row a duplicate? Same time? same date? all columns being the same?
If you have a primary key you can use the TOP function to select only one record and delete that one row:
Delete from [tablename] where id in (select top 1 id from [tablename] where [clause])

Answer 4

If you don't mind the order of these rows there is a command in MySQL:
DELETE TOP (numberOfRowsToDelete) FROM db.tablename WHERE {condition for ex id = 5};

Answer 5

Since I don't have the schema, I'd a possible solution in steps:
Apply a row number to the select of all columns
Make a group by with those columns and delete the min(rownumber) in each group
Edit:
The rownumber is in a inner query and will have the rownumber incrementing in all rows. In the outer query I make the group by of the inner query and select the min(rownumber) for each group. Since each group is composed by duplicated rows, I then remove the min(rownumber) for each group.

Answer 6

using LIMIT 1 will help you delete only 1 ROW that matches your DELETE query:
DELETE FROM `table_name` WHERE `column_name`='value' LIMIT 1;
BEFORE:
+----------------------+
| id | column_name |
+-----+----------------+
| 1 | value |
+-----+----------------+
| 2 | value |
+-----+----------------+
| 3 | value |
+-----+----------------+
| 4 | value |
+-----+----------------+
AFTER:
+----------------------+
| id | column_name |
+-----+----------------+
| 1 | value |
+-----+----------------+
| 2 | value |
+-----+----------------+
| 3 | value |
+-----+----------------+