图书馆有时会对某图书的复本量进行更新，如增购某图书

-- 复本，或因各种原因导致某图书丢失部分复本。复本量的更改直接导致库

-- 存量的改变，但为了不因误操作破坏数据完整性，我们不能对库存量直接

-- 修改，可以通过触发器，监测复本量的改变，自动修改库存量，这就可以

-- 用到对选定列的更新进行监测的方法。-Library books sometimes have a copy of the volume of updates, such as the purchase of a book- a copy of, or for various reasons leading to the loss of part of a copy of a book. A copy of a direct result of changes in the volume of the Treasury- the stock of the changes, but in order not to damage due to misoperation data integrity, we can not directly on the stock- to amend, you can flip-flop, monitoring changes in the volume of copy, automatic modification inventory levels, which can- to use an updated list of selected monitoring methods.