Use this statement to begin a user-defined transaction.
BEGIN TRAN[SACTION] [ transaction-name ]
The optional parameter transaction-name is the name assigned to this transaction. It must be a valid identifier. Use transaction names only on the outermost pair of nested BEGIN/COMMIT or BEGIN/ROLLBACK statements.
When executed inside a transaction, the BEGIN TRANSACTION statement increases the nesting level of transactions by one. The nesting level is decreased by a COMMIT statement. When transactions are nested, only the outermost COMMIT makes the changes to the database permanent.
Both Adaptive Server Enterprise and SQL Anywhere have two transaction modes.
The default Adaptive Server Enterprise transaction mode, called unchained mode, commits each statement individually, unless an explicit BEGIN TRANSACTION statement is executed to start a transaction. In contrast, the ISO SQL/2003 compatible chained mode only commits a transaction when an explicit COMMIT is executed or when a statement that carries out an autocommit (such as data definition statements) is executed.
You can control the mode by setting the chained database option. The default setting for ODBC and embedded SQL connections in SQL Anywhere is On, in which case SQL Anywhere runs in chained mode. (ODBC users should also check the AutoCommit ODBC setting). The default for TDS connections is Off. See chained option [compatibility].
In unchained mode, a transaction is implicitly started before any data retrieval or modification statement. These statements include: DELETE, INSERT, OPEN, FETCH, SELECT, and UPDATE. You must still explicitly end the transaction with a COMMIT or ROLLBACK statement.
You cannot alter the chained option within a transaction.
When calling a stored procedure, you should ensure that it operates correctly under the required transaction mode.
The current nesting level is held in the global variable @@trancount. The @@trancount variable has a value of zero before the first BEGIN TRANSACTION statement is executed, and only a COMMIT executed when @@trancount is equal to one makes changes to the database permanent.
A ROLLBACK statement without a transaction or savepoint name always rolls back statements to the outermost BEGIN TRANSACTION (explicit or implicit) statement, and cancels the entire transaction.
SQL/2003 Vendor extension.
The following batch reports successive values of @@trancount as 0, 1, 2, 1, and 0. The values are printed on the database server messages window.
PRINT @@trancount BEGIN TRANSACTION PRINT @@trancount BEGIN TRANSACTION PRINT @@trancount COMMIT PRINT @@trancount COMMIT PRINT @@trancount
You should not rely on the value of @@trancount for more than keeping track of the number of explicit BEGIN TRANSACTION statements that have been issued.
When Adaptive Server Enterprise starts a transaction implicitly, the @@trancount variable is set to 1. SQL Anywhere does not set the @@trancount value to 1 when a transaction is started implicitly. Consequently, the SQL Anywhere @@trancount variable has a value of zero before any BEGIN TRANSACTION statement (even though there is a current transaction), while in Adaptive Server Enterprise (in chained mode) it has a value of 1.
For transactions starting with a BEGIN TRANSACTION statement, @@trancount has a value of 1 in both SQL Anywhere and Adaptive Server Enterprise after the first BEGIN TRANSACTION statement. If a transaction is implicitly started with a different statement, and a BEGIN TRANSACTION statement is then executed, @@trancount has a value of 2 in both SQL Anywhere, and Adaptive Server Enterprise after the BEGIN TRANSACTION statement.
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