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How to update a row with another row if column values are null in SQL

, 17 Aug 2012 CPOL
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Update row column with another row column in same table SQL only if it is null.


If you need to update one row columns from another row columns in the same table following approach can be useful.


To test queries and concept I am using SQL Server 2008 R2.


Create a sample table.

CREATE TABLE [dbo].[Employee](
[Title] [varchar](50) NULL,
[FirstName] [varchar](50) NULL,
[Surname] [varchar](50) NULL,
[DOB] [varchar](50) NULL,
[Datestarted] [varchar](50) NULL,
[EmployeeId] [int] IDENTITY(1,1) NOT NULL,
[Interest] [varchar](50) NULL,
[EmpAddress] [varchar](500) NULL

Add some sample rows as follows.

I am just updating 2 columns. Of course you can update more in similar fashion. Here updating two columns of 1st row with 2nd row column values.

SET n.EmpAddress = p.EmpAddress
,n.[Interest] = p.Interest
FROM [Employee] n inner join [Employee] p
ON n.employeeid = 1 AND p.employeeid = 2
Select * from Employee

Please see next query if you wish to update only when value in the column is null.

Update column when value is null

I am going to use COALESCE. This is function similar to Case.

It returns the first nonnull expression among its arguments. Example:

select coalesce(Interest,'FUN') from [Employee] where EmployeeId = 5 

Updating two columns of row 4th when they are null with column values of row 3rd.

Precise query can look like

SET n.EmpAddress = coalesce(n.EmpAddress, p.EmpAddress)
,n.[Interest] = coalesce(n.Interest, p.Interest)
FROM [Employee] n inner join [Employee] p
ON n.employeeid = 4 AND p.employeeid = 3
Select * from Employee


In this article I have suggested queries to update row with anther row and how you can use coalesce to restrict modification to null fields only. I hope you can use these queries for other purposes too.


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

United States United States
Manoj Kumar

Architect, Lead Software Engineer and Senior BI Developer | Microsoft Certified Technology Specialist(MCTS) | Exp in C#, ASP.Net, MVC, Razor View Engine and EF Code First, HTML5, CSS3, JQuery, Javascript, AngularJS, JSON, AJAX, KnockoutJS, Silverlight, WPF, WCF, WF, SSRS, SSAS, SSIS, ETL, SQL Server, Usability/User Experience etc.

He lives with his wife Supriya and daughter Tisya in Bay Area.

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Comments and Discussions

Suggestiongood one Pin
Rajesh Varma Buddaraju22-May-14 1:25
memberRajesh Varma Buddaraju22-May-14 1:25 

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