SQL 2008 how to compare & identify data among 2 tables with same structure ?

Question

Hello is there a TSQL way of comparing row by row for example comparing DateTimeStamp field in 2 separate tables with same structure in identifying if it's data was changed (If Table1.DateField > Table2.DateField THEN UPDATE it's entire row to match it's
corresponding Table1 row.) ?
Probably thinking would need a cursor to loop through or are there other better ways via TSQL ?
Thanks in advance.

Answer 1

Hi,
I am assuming you have a PRIMARY KEY field or a UNIQUE field in both tables, which you should!
You can do this using "UPDATE with INNER JOIN". (SQL Server – Update Table with INNER JOIN)
Working example:
USE [TestDatabase]
GO
/* Create Temp Tables */
CREATE TABLE [dbo].[Table1]
[ID] INT
,[Name] VARCHAR(10)
,[ModifyDate] DATETIME
CREATE TABLE [dbo].[Table2]
[ID] INT
,[Name] VARCHAR(10)
,[ModifyDate] DATETIME
GO
INSERT INTO [dbo].[Table1] ([ID], [Name], [ModifyDate]) VALUES (1, 'Vishal', GETDATE())
INSERT INTO [dbo].[Table2] ([ID], [Name], [ModifyDate]) VALUES (1, 'Gajjar', GETDATE() + 1)
GO
SELECT [ID], [Name], [ModifyDate] FROM [dbo].[Table1]
SELECT [ID], [Name], [ModifyDate] FROM [dbo].[Table2]
GO
UPDATE T1
SET T1.[Name] = T2.[Name]
FROM [dbo].[Table1] T1
INNER JOIN [dbo].[Table2] T2 ON T1.[ID] = T2.[ID] /* Join on Key field */
WHERE T2.[ModifyDate] > T1.[ModifyDate] /* Update criteria */
GO
/* CleanUp - Drop Tables
DROP TABLE [dbo].[Table1], [dbo].[Table2]
This Updates Table1 with latest values from Table2, You need to change the UPDATE statement for your scenario.
- Vishal
SqlAndMe.com