If the operation occurs in an unchecked context, the result is truncated by discarding any high-order bits that do not fit into the destination type.
如果操作发生在未检查的上下文中，计算的结果被截断，放弃不适合目标类型的任何高序位。
2
Additionally, there cannot be a foreign key constraint between the table being truncated and other tables, otherwise the truncate table operation fails.