HEIDENHAIN MANUALplus 620 Technical Manual page 1623

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Concluding the

January 2012

Be sure to conclude every transaction. This way the resources assigned in the

SQL server are released for the result set.

After concluding the transaction with SQL COMMIT, all changes are

transferred from the result set into the table.

To cancel all changes, conclude the transaction with SQL ROLLBACK.

Once transferred, these changes cannot be undone. After the transaction has

been completed, the rows locked during the selection are unlocked.

The transaction to be completed is identified by the handle. After the

transaction has been completed successfully, the handle becomes invalid and

cannot be used for accessing data any longer.

The result of the SQL COMMIT function will not be 0 if the edited data could

not be transferred into the table file. This happens when edited rows were not

locked during the selection and are locked by third parties at the time of

commitment. The SQL server first checks whether all edited rows may be

rewritten before it transfers the first change. The isolation of accesses

ensures that the effects of the transaction are invisible to others until the

transaction is committed. It may, however, happen that errors occur while a

file is being accessed.

The SQL ROLLBACK function enables you to remove all rows, except for the

indicated row, from the result set by defining an index. As a result, the

changes made to the removed rows are canceled. This is especially useful if

you first select and, as a consequence, lock more than one row, but then

decide that you want to edit only one row. The other rows can then

immediately be released. The handle remains effective until the transaction

has been completed for all rows. If no index or an invalid index has been

defined, the entire transaction is completed. The result of the function does

not equal 0 if an error has occurred.