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Effect of transactional statements on @@trancount
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SQL Server 2000 Stored Procedure Programming
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In fact, if you execute an additional Rollback Transaction statement after the first one, SQL Server will report an error (see Figure 6-4).
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TIP: I have to admit that I had many problems with this issue at one time. Be careful.
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To prevent this error, you need to test for the value of the @@trancount variable before you execute the Rollback Transaction statement. A simple way to test for this value could work something like this:
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if @@trancount > 0 Rollback Transaction
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Figure 6-4.
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Effect of the Rollback Transaction statement on @@trancount
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Composite Transact-SQL Constructs Batches, Scripts, and Transactions
Named Transactions
Transaction statements can be named. The name must be a valid SQL Server identifier (that is, no more than 128 characters), but SQL Server will read only the first 32 characters:
Begin Tran[saction][transaction_name|@transaction_name_variable] Commit Tran[Saction][transaction_name|@transaction_name_variable] Rollback [Tran[saction][transaction_name|@transaction_name_variable]]
I know that this sounds like a perfect tool for resolving some issues with nested transactions. Unfortunately, in nested transactions, only the names of outer transactions are recorded by SQL Server. If you try to roll back any of the inner transactions, errors occur. Figure 6-5 provides an academic demonstration of such an attempt.
Figure 6-5.
Named transactions
SQL Server 2000 Stored Procedure Programming
TIP: From Figure 6-5, you can see that you need to know the name of the outer transaction that has called all other stored procedures/transactions. This is not a practical requirement, especially when your stored procedure will be called from more than one stored procedure. Therefore, I recommend that you do not use transaction names.
Savepoints
SQL Server contains a mechanism for canceling part of a transaction. This statement may seem to contradict the basic idea of a SQL Server transaction as I have explained it, but it can be justified in some cases (for example, in the case of bad connections or if an operation has a low probability of success). The mechanism is known as a savepoint. To mark a savepoint in a transaction, use the following statement:
Save Tran[saction]{savepoint_name|@savepoint_variable}
The savepoint s name is also a SQL Server identifier, but SQL Server reads only the first 32 characters. Savepoints do not save anything to the database. They just mark the point to which you can roll back a transaction. Resources (like locks) also stay in place after a Save Transaction statement. They are released only when a transaction has been completed or canceled. The following procedures are designed to store an order and set of order items in a database. The prScrapOrderSaveItem stored procedure uses savepoints to roll back the insertion of a particular item.
Create Procedure prScrapOrder -- save order information. @dtsOrderDate smalldatetime, @intRequestedById int, @dtsTargetDate smalldatetime, @chvNote varchar(200), @insOrderTypeId smallint, @inyOrderStatusId tinyint As
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Composite Transact-SQL Constructs Batches, Scripts, and Transactions
Set nocount on Insert [Order](OrderDate, TargetDate, Values (@dtsOrderDate, @dtsTargetDate, @insOrderTypeId, Return @@identity Go Create Procedure prScrapOrderSaveItem -- Saves order item. -- If error occurs, this item will be rolled back, -- but other items will be saved. -- demonstration of use of Save Transaction -- must be called from sp or batch that initiates transaction @intOrderId int, @intInventoryId int, @intOrderItemId int OUTPUT As Set nocount on Declare @intErrorCode int, @chvInventoryId varchar(10) -- name the transaction savepoint Set @chvInventoryId = Convert(varchar, @intInventoryId) Save Transaction @chvInventoryId -- Set value of Lease of all equipment associated -- with expired Lease Schedule to 0 Insert OrderItem (OrderId, InventoryId) Values (@intOrderId, @intInventoryId) RequestedById, Note, @intRequestedById, @chvNote, @inyOrderStatusId)
OrderTypeId, OrderStatusId)
SQL Server 2000 Stored Procedure Programming
Select @intOrderItemId = @@identity, @intErrorCode = @@Error If @intErrorCode <> 0 Begin Rollback Transaction @chvInventoryId Return @intErrorCode End Return 0 Go
The following script demonstrates how an application using these stored procedures must initiate a transaction:
Declare @intOrderId int, @intOrderItemId int Begin Tran Exec @intOrderId = prScrapOrder @dtsOrderDate = '1/10/1999', @intRequestedById = 1, @dtsTargetDate = '1/1/2000', @chvNote = NULL, @insOrderTypeId = 3, -- scrap @inyOrderStatusId = 1 -- ordered Exec prScrapOrderSaveItem @intOrderId, 11, @intOrderItemId OUTPUT Exec prScrapOrderSaveItem @intOrderId, 5, @intOrderItemId OUTPUT Exec prScrapOrderSaveItem @intOrderId, 7, @intOrderItemId OUTPUT Commit Tran
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