If you are updating multiple rows in one statement, but only want to update a value in a column if a condition is satisfied, then you need to perform some sort of if logic inside your update. Here’s a straight forward way of doing this.
In the example below, I am just going to use 2 temp table variables. I’ll update the @SourceTable with the data from the @UpdateTable… but only where the UpdateFlag field is set to 1.
In the example above, you can see that the AnimalName is only updated when the UpdateFlag column is set to 1. The 2nd record “Cat” is not updated with the value “Cow” because it has a 0 for the UpdateFlag. This is done using a case statement on the SET operation. The example above is very simple. This case logic in the SET operation becomes much more helpful in more complex queries.
The OUTPUT clause is an amazing part of SQL Server that many people do not know about. As corny as it is, I still remember the day that I found it. I had been searching for the whole day trying to figure out how to get the identity values from a large amount of data that I just inserted in to the database. There had to be a way… right? After searching and searching, I gave up and just accepted that it is not possible… a few days later I found exactly what I was looking for… the OUTPUT clause.
The OUTPUT clause is a part of the query that will return data from before or after the operations is completed. Let’s say that you inserted data in to a table and you wanted the ID column values (which are auto-numbers). The OUTPUT clause gives you this information! It can work on INSERT, DELETE, UPDATE, and MERGE statements. I will take you through examples of each.
To access the data that is being altered in your sql statement, you need to use special column prefixes that SQL Server makes available to you. The two special prefixes are “inserted” and “deleted”. During an insert statement, the inserted prefix is available for you to use. During a delete statement, the deleted prefix is available to you. During the update and merge statements, both the deleted and inserted prefixes are available to you. In these cases, the deleted represents the data before it was changed and the inserted represents the data after it was changed.
One thing to note is that the data being outputted must go in to a table or table variable.
OUTPUT Clause On An INSERT Statement
-- Insert into the table and stick the resulting animal
This part says to parse the @XMLToParse variable (previously filled with the XML file) using the method built in to SQL Server called .nodes. It specifies the repeating node to be Animals/LandAnimals/Animal. It assigns an aliases this XML parsed records as a table named xmlData. The (A) is the column name of the rowset. This will be referenced in the select part of the statement.
The select part of this statement references xmlData (which is the table aliases) and A (which is the column named for that table). It calls the .value function to return the value from the table/column. For the .value function, you pass in 2 elements.
The first element is the field. In this case we are passing in just a period. We do this because there is no node below the Animal node. If there was, we would need to specify it here..
The second parameter is the datatype that you would like the value to be casted as. Then I always aliases the field to something relevant.
Although parsing XML can be a little confusing in SQL Server, it is very powerful. This is a great way to pass bulk data to a stored procedure from any type of client application.