在python中将字符串作为变量调用(calling string as variable in python)

 与事务类似，语句也是原子的。 一旦语句开始执行数据更改，就会保存原始状态（实际上会记录更改）。 如果语句因任何原因失败（超时，与刚刚提交的事务冲突），则必须将更改恢复为原始状态。 该语句将报告失败但事务仍处于打开状态，您可以继续执行该事务，就像从未执行过该语句一样。 
 
 这实际上类似于保存点 - 您可以想象在记录每个语句保存点之前和语句完成之后，保存点已提交。 但是，这对外部事务或保存点没有影响。 

Similarly to transaction, statement is atomic as well. Once the statement starts performing the data changes, the original state is saved (actually the changes are recorded). If statement fails for whatever reason (timeout, conflict with just committed transaction) the changes must be reverted to the original state. The statement will report a failure but the transaction is still open and you can continue with the transaction just like the statement was never executed.
 
This is actually similar to savepoint - you can imagine that before each statement savepoint is recorded and after statement is completed, the savepoint is committed. This has no influence on outer transaction or savepoints however.