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This article introduces the relevant knowledge of "what are the new sentences in SQLServer2008". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

When synchronizing information between two tables, there are three steps that must be performed. First of all, you have to deal with any new rows that need to be inserted into the target data table. The second is to deal with existing rows that need to be updated. Finally, delete the old lines that are no longer used. This process requires a lot of repetitive logic to be maintained and can lead to subtle errors.

What is worth our attention is that BobBeauchemin discusses the MERGE statement, which combines the above steps into a single statement. The following is an example given by him:

Here is a snippet of the quote:

Merge[target] t

Using[source] sont.id=s.id

Whenmatchedthenupdatet.name=s.name,t.age=s.age--use "rowset1"

Whennotmatchedtheninsertvalues (id,name,age)-use "rowset2"

Whensourcenotmatchedthendelete;--use "rowset3"

What are the new statements in SQLServer2008

As you can see, the specific operation is determined based on the parsing results of the following join. In this example, if the target and source data table have matching rows, the update operation is performed. If not, insert or delete operations are performed to make the target data table consistent with the source data table.

One of the subtleties of this new syntax is its certainty in dealing with updates. When using standard UPDATE syntax and unions, there may be more than one source line matching the target line. In this case, it is impossible to predict which source row of data will be used in the update operation.

When we use MERGE syntax, if there is more than one match, it throws an error. This requires the idea of developers, in order to achieve the desired goals, the current joint conditions are not very clear.

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