Sunday T-SQL tip: Temporary table variables and transaction context

Recently I’ve been asked if it’s possible to partially commit the transaction. Interestingly enough – the answer is not simple. SQL Server does not support nested transactions. Although there are a few tricks you can use.

First is savepoints. This will allow you to save transaction state at some point, rollback to that point and commit everything you did prior that point. Obviously it will help you to commit only first (beginning) part of the transaction.

Let’s see it in action. Let’s create the small table.

Next, let see savepoints in action.

Good. Now assumming we would like to do opposite task – commit the “tail’ actions after specific point. Unfortunately you cannot do it with regular T-SQL statements. Fortunately there is the trick – temporary table variables. They are not supporting transaction context. Let’s see it in action:

As you can see, you can create temporary table variable, populate it with data, rollback the transaction and next save data in the separate transaction. It worth to mention that regular temporary tables do not work that way – they fully support transaction context.

One of the practical usage of this scenario is audit on rollback. You can save required data into temp table variable, rollback data modification attempt and write audit information to the audit table.

P.S. Just wonder if anybody reads it πŸ™‚

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