The SQL MERGE statement was introduced in SQL Server 2008 and allows you to modify data in a target table based on data in a source table in one easy statement, replacing lots of messy code.  I use it frequently when building a data warehouse.

In short, the statement joins the target to the source by using a column common to both tables, such as a primary key.  You can then insert, modify, or delete data from the target table—all in one statement—according to how the rows match up as a result of the join.

I highly recommend becoming familiar with the MERGE statement as you will find yourself using it frequently.

Here is an example use of the MERGE statement:

MERGE [MD-Cache].[GRD].[TblContinent] AS target
USING (SELECT SlbMasterData_PK, Name, SourceID, ContinentCode, GRDStatus, ModifiedBy, ModifiedDate FROM [MDS2012].[mdm].[vGRD_TblContinent])
		AS source (SlbMasterData_PK, Name, SourceID, ContinentCode, GRDStatus, ModifiedBy, ModifiedDate)
ON (target.SlbMasterData_PK = source.SlbMasterData_PK)
--record is in source as well as target, only update in target if a field has changed or status in target is "DEPRECATED"
WHEN MATCHED AND (target.Name <> source.Name OR target.SourceID <> source.SourceID OR target.Code <> source.ContinentCode OR target.GRDStatus <> source.GRDStatus
					OR target.ModifiedBy <> source.ModifiedBy OR target.ModifiedDate <> source.ModifiedDate OR target.MasterDataStatus_FK = 'DEPRECATED') THEN
	UPDATE
	SET target.Name = source.Name, target.SourceID = source.SourceID, target.Code = source.ContinentCode,
			target.GRDStatus = source.GRDStatus, target.ModifiedBy = source.ModifiedBy, target.ModifiedDate = source.ModifiedDate, target.MasterDataStatus_FK='ACTIVE'
--record is in source but not target, so insert into target
WHEN NOT MATCHED BY TARGET THEN
	INSERT (Name, SourceID, Code, SlbMasterData_PK, MasterDataStatus_FK, GRDStatus, ModifiedBy, ModifiedDate)
		VALUES (source.Name, source.SourceID, source.ContinentCode, source.SlbMasterData_PK, 'ACTIVE', 'APPROVED', 'Org-by', getdate())
--record has been deleted from source...don't delete it in target but rather mark the status in target as "DEPRECATED" (if it is not already)
WHEN NOT MATCHED BY SOURCE AND (target.MasterDataStatus_FK <> 'DEPRECATED') THEN
	UPDATE
	set target.MasterDataStatus_FK = 'DEPRECATED'
--display results of MERGE
OUTPUT $action, Deleted.SlbMasterData_PK, Inserted.SlbMasterData_PK, Deleted.SourceID, Inserted.SourceID, Deleted.Code, Inserted.Code,
	Deleted.GRDStatus, Inserted.GRDStatus, Deleted.MasterDataStatus_FK, Inserted.MasterDataStatus_FK, Deleted.ModifiedDate, Inserted.ModifiedDate, Deleted.ModifiedBy, Inserted.ModifiedBy;
;
 

More info:

MERGE Statement Generator

MERGE gives better OUTPUT options

What is the T-SQL Merge Statement and How do you use it?

The MERGE Statement in SQL Server 2008

Be Careful with the Merge Statement

Optimizing MERGE Statement Performance

Stairway to T-SQL DML Level 12: Using the MERGE Statement

Avoiding the Halloween Problem with MERGE

Using the SQL Server MERGE Statement to Process Type 2 Slowly Changing Dimensions

A Hazard of Using the SQL Merge Statement

Writing T-SQL Merge Statements the Right Way

How to Properly Load Slowly Changing Dimensions using T-SQL Merge

Performance of the SQL MERGE vs. INSERT/UPDATE