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; ;