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/2008 compatible chained
mode only commits a transaction when an explicit COMMIT is executed or when a statement that carries out an autocommit (such
as a data definition statement) 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.
In unchained mode, a transaction is implicitly started before any data retrieval or manipulation statement. These statements
include: DELETE, INSERT, OPEN, FETCH, SELECT, and UPDATE. You must still explicitly end the transaction with a COMMIT or ROLLBACK
You cannot alter the setting of 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.
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 executed.
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. Instead, 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.
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.