Titlebook: Inside Relational Databases with Examples in Access; Mark Whitehorn,Bill Marklyn Book 2007 Springer-Verlag London Ltd. 2007 Access.SQL.arc

无弹性

Induction

Queries/ViewsCreating a database and then entering all the data takes time and effort. Simply creating a database is not an end in itself; unless you are one of those sad people (like me) who actually enjoys that sort of thing, there has to be some gain for the pain. That gain lies in the easy access to the data provided by an electronic database.

tangle

FormsData resides in the tables, but a database is more than simply data. It also includes components that are used as tools to look at, enter, delete and manipulate that data. Those components are called forms.

胆小鬼

Introduction to Part 2So far we have confined ourselves to databases based upon a single table of data. These are great for learning about databases and occasionally the data you meet in the real world will actually fit neatly into just one table. For example, I once built a single-table database for SHARP (Scottish Heart and Arterial disease Risk Prevention).

有常识

Multiple tables cure serious problemsSo, let’s have a look at the way in which multiple tables can remove these problems.

描绘

How are relationships modeled?OK, so we’ve got our objects — employees, customers, orders etc. — nicely represented as tables in the database. We now understand the relationships that can exist between these objects. The next step is to see how we can model the relationships in the database.

外露

Revisiting the big four — the synergy beginsIn this part we have been looking at why single tables are bad, why multiple tables are good and latterly at how you actually arrange the data into separate tables. Now seems like a good time to look at the gains you get from splitting up data in this way.

Simulate

IntegrityHow accurate should the data in a database be? 100% would be good, of course, but what is realistically acceptable in a database of reasonable size? 90%? 95%? The answer is that we need to go much higher than 95% for one very simple reason.

不足的东西

Initial

Introductionor the end is reached of what I now confess to have been 24 pages of deceit. I have disguised under the designation of Chapter One what was really nothing more than an introduction; but I know quite well, that had I been honest and called it an introduction, nobody would have read it.”