begin transaction/rollback transaction

http://msdn.microsoft.com/en-us/library/ms188929.aspx

BEGIN TRANSACTION represents a point at which the data referenced by a connection is logically and physically consistent. If errors are encountered, all data modifications made after the BEGIN TRANSACTION can be rolled back to return the data to this known state of consistency. Each transaction lasts until either it completes without errors and COMMIT TRANSACTION is issued to make the modifications a permanent part of the database, or errors are encountered and all modifications are erased with a ROLLBACK TRANSACTION statement.

BEGIN TRANSACTION starts a local transaction for the connection issuing the statement. Depending on the current transaction isolation level settings, many resources acquired to support the Transact-SQL statements issued by the connection are locked by the transaction until it is completed with either a COMMIT TRANSACTION or ROLLBACK TRANSACTION statement. Transactions left outstanding for long periods of time can prevent other users from accessing these locked resources, and also can prevent log truncation.

Although BEGIN TRANSACTION starts a local transaction, it is not recorded in the transaction log until the application subsequently performs an action that must be recorded in the log, such as executing an INSERT, UPDATE, or DELETE statement. An application can perform actions such as acquiring locks to protect the transaction isolation level of SELECT statements, but nothing is recorded in the log until the application performs a modification action.

--------------------

http://msdn.microsoft.com/en-us/library/ms181299.aspx

In stored procedures, ROLLBACK TRANSACTION statements without a savepoint_name or transaction_name roll back all statements to the outermost BEGIN TRANSACTION. A ROLLBACK TRANSACTION statement in a stored procedure that causes @@TRANCOUNT to have a different value when the stored procedure completes than the @@TRANCOUNT value when the stored procedure was called produces an informational message. This message does not affect subsequent processing.

@@TRANCOUNT is incremented by one when entering a trigger, even when in autocommit mode. (The system treats a trigger as an implied nested transaction.)

Sample：

BEGIN TRY
    BEGIN TRANSACTION 
       insert into [chsAoffline]..[ABC] select * from [chsA]..[ABC] where callid not in (select callid from call)
       delete from [CHSA]..[ABC] where callid in (select distinct(callid) from [chsAoffline]..[ABC])
    COMMIT
END TRY
BEGIN CATCH

    IF @@TRANCOUNT > 0
        ROLLBACK
END CATCH