Update a single row with t-sql

I want to update a row in my date base. The problem is, through开发者_Python百科 a mistake on my part, I have two identical rows of data. How do I run the update on just one row?

In SQL Server 2005+, you can use

UPDATE TOP (1) ....

The advantage of this over SET ROWCOUNT is that any triggers will not be subject to a ROWCOUNT limit, which is almost certainly a good thing.

Often tables have a unique ID. And you should filter on that.

For example,

UPDATE YourTable
SET YourColumnToUpdate = 'your_value'
WHERE YourUniqueColumn = @Id

If your table does not have a unique ID, consider adding one: an integer column with a Primary Key and Identity.

I suggest you go back and normalize your database. At the very least add a auto increment int primary key column and use that id. Using UPDATE TOP 1 might work and directly answers your question, but non - normalization of your database is the "real" problem.

http://en.wikipedia.org/wiki/Database_normalization

Use SET ROWCOUNT;

SET ROWCOUNT 1; UPDATE Production.ProductInventory SET Quantity = 400 WHERE Quantity < 300; GO

http://msdn.microsoft.com/en-us/library/ms188774.aspx

-- 01. create the table for the test-data
CREATE TABLE dbo.Orders (
    ID INTEGER
    ,Value DECIMAL(10, 2)
    ,Descr NVARCHAR(100)
    ,BookingDate DATETIME
    ,UserName NVARCHAR(100)
    ,CountMeasure INTEGER
)

-- 02. save the timestamp for the inserts
DECLARE @date AS DATETIME
SET @date = getdate()

-- 03. inserting test-data
INSERT INTO dbo.Orders VALUES (1,499.99,'Notebook',@date,'tgr',0)
INSERT INTO dbo.Orders VALUES (2,650.00,'PC',@date,'tgr',0)
INSERT INTO dbo.Orders VALUES (3,29.50,'Keyboard',@date,'tgr',0)

-- 04. adding the duplicate entry
INSERT INTO dbo.Orders VALUES (2,650.00,'PC',@date,'tgr',0)

-- 05. viewing the 4 Rows
SELECT * FROM dbo.Orders

-- 06. viewing the distinct 3 Rows
SELECT DISTINCT * FROM dbo.Orders

/* You don't want to delete the duplicate row, but you want to count 
   the distinct IDs using SUM on the CountMeasure-Column */

-- 07. alternativ solution (which may does not fit your requirements)
/* So your result shoud be the same like this */
SELECT COUNT(DISTINCT ID) as DistinctCount
FROM dbo.Orders

-- 08. Understanding the solution
/* To understand the solution we take a look on the main-part 
   We generate for each ID a Row-Number ordered by random  
   Details: https://msdn.microsoft.com/de-de/library/ms186734%28v=sql.120%29.aspx */
SELECT * , ROW_NUMBER() OVER (PARTITION BY ID ORDER BY NEWID()) AS RowNumberForEachId
FROM dbo.Orders

-- 09. The update statement
/* We use this part to update our table */
UPDATE a
SET CountMeasure = 1
FROM (-- Orders incl
      SELECT * , ROW_NUMBER() OVER (PARTITION BY ID ORDER BY NEWID()) as rowNum
      FROM dbo.Orders
) as a
WHERE rowNum = 1

-- 10. Viewing the Result 
SELECT * FROM dbo.Orders 

-- 11. Comparing Count(DISTINCT ...) with the SUM(...) alternative
SELECT COUNT(DISTINCT ID) as countDistinct, SUM(CountMeasure) as sumCountMeasure
FROM dbo.Orders

-- 12. Removing the test-table
DROP TABLE dbo.Orders