问题 单项选择题

关于触发器trigger,下面说法不正确的是

A.触发器是定义在表上的

B.触发器名称在数据库中必须是唯一的

C.触发器对应于一组SQL语句

D.每张表限制定义一个触发器

答案

参考答案:D

解析: 触发器采用事件驱动机制,当某个触发事件发生时,触发器触发一系列操作。触发器是一种特殊类型的存储过程,当一个触发器建立后,它作为一个数据库对象被存储。触发器定义在表一级,它与指定的数据修改操作相对应。在一个表上可以建立多个名称不同、类型各异的触发器。

多项选择题
单项选择题

For many people today, reading is no longer relaxation. To keep up their work they must read letters, reports, trade publications, interoffice communications, not to mention newspapers and magazines: a never ending flood of words. In (1) a job or advancing in one, the ability to read and comprehend (2) can mean the difference between success and failure. Yet the unfortunate fact is that most of us are (3) readers. Most of us develop poor reading (4) at an early age, and never get over them. The main deficiency (5) in the actual stuff of language itself—words. Taken individually, words have (6) meaning until they are strung together into phrases, sentences and paragraphs. (7) , however, the untrained reader does not read groups of words. He laboriously reads one word at a time, often regressing to (8) words or passages. Regression, the tendency to look back over (9) you have just read, is a common bad habit in reading. Another habit which (10) down the speed of reading is vocalization—sounding each word either orally or mentally as (11) reads.

To overcome these bad habits, some reading clinics use a device called an (12) , which moves a bar(or curtain) down the page at a predetermined speed. The bar is set at a slightly faster rate (13) the reader finds comfortable, in order to "stretch" him. The accelerator forces the reader to read fast, (14) word by word reading, regression and subvocalization practically impossible. At first (15) is sacrificed for speed. But when you learn to read ideas and concepts, you will not only read faster, (16) your comprehension will improve. Many people have found (17) reading skill drastically improved after some training. (18) Charlie Au, a business manager, for instance. His reading rate was a reasonably good 172words a minute (19) the training; now it is an excellent 1,378 words a minute. He is delighted that how he can (20) a lot more reading material in a short period of time.

第(1)空应选择()

A.applying

B.doing

C.offering

D.getting