Get Smart at ruthenpress.info ruthenpress.info makes your life easier with 1,s of answers on everything from removing wallpaper to using the. to succeed in college The book you are holding in your hands is now in its seventh edition,. How to Study Java The Complete Reference - 7th Edition. SQL For Dummies, 7th Edition, shows programmers and web developers how to use SQL to build relational databases and get valuable information from them.
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SQL For Dummies, 7th Edition. Book Details. Related Book. SQL For Dummies, 8th Edition - pdf - Free IT eBooks Download. • Jump right in—without previous. Yumpu PDF Downloader. SQL for Dummies 7th Edition. SQL for Dummies 7th Edition. Print as pdf. All rights reserved to ruthenpress.info Updated for the latest SQL functionality, SQL For Dummies, 8th Edition covers the core SQL language and shows you how to use SQL to structure a DBMS.
An enterprise database can be huge. Enterprise databases maymodel the critical information flow of entire large organizations. Glad you asked. A database management system DBMS is a set of programsused to define, administer, and process databases and their associatedapplications. The database being managed is, in essence, a structure that youbuild to hold valuable data.
A DBMS is the tool you use to build that structureand operate on the data contained within the database. You can find many DBMS programs on the market today. Some run only onmainframe computers, some only on minicomputers, and some only onpersonal computers. A strong trend, however, is for such products towork on multiple platforms or on networks that contain all three classes ofmachines. An even newer trend is to distribute data over a storage areanetwork SAN or even to store it out on the Internet.
A DBMS that runs on platforms of multiple classes, large and small, is calledscalable.
Whatever the size of the computer that hosts the database — and regardlessof whether the machine is connected to a network — the flow of informationbetween database and user is always the same. Figure shows that theuser communicates with the database through the DBMS.
The DBMS masksthe physical details of the database storage so that the application only hasto concern itself with the logical characteristics of the data, not with how thedata is stored.
Ouratoms combine into enzymes, proteins, hormones,and many other substances that wouldcost millions of dollars per ounce on the pharmaceuticalmarket. The precise structure ofthese combinations of atoms is what gives themgreater value. By analogy, database structuremakes possible the interpretation of seeminglymeaningless data.
The structure brings to thesurface patterns, trends, and tendencies in thedata.
Unstructured data — like uncombinedatoms — has little or no value. Flat FilesWhere structured data is concerned, the flat file is as simple as it gets. Flat filesare so called because they have minimal structure. A flat file is simply a collection ofdata records, one after another, in a specified format — the data, the wholedata, and nothing but the data — in effect, a list. In computer terms, a flat fileis simple. The system may have a structure somethinglike this:Harold Percival S.
Each field has a fixedlength the Name field, for example, is always exactly 15 characters long , andno structure separates one field from another. The person who created thedatabase assigned field positions and lengths. Such low overhead means that operating on flat files can be very fast.
The application mustknow exactly where and how the file stores its data. Thus, for small systems,flat files work fine. The larger a system is, however, the more cumbersome aflat-file system becomes.
Using a database instead of a flat-file system eliminates duplication of effort. Although database files themselves may have more overhead, the applicationscan be more portable across various hardware platforms and operatingsystems.
Databases eliminate duplication of effort, because the DBMS handles thedata-manipulation details. Applications written to operate on flat files mustinclude those details in the application code. If multiple applications allaccess the same flat-file data, these applications must all redundantly include that data-manipulation code. Clearly, if a flat-file-based application includes data-manipulation code thatonly runs on a particular hardware platform, migrating the application to anew platform is a headache waiting to happen.
Migrating a similarDBMS-based application to another platform is much simpler — fewercomplicated steps, fewer aspirin consumed. They suffer from redundancy problemsand their structural inflexibility makes database modification difficult. Nowadays, new installations of database managementsystems are almost exclusively of the relational type.
Organizations thatalready have a major investment in hierarchical or network technologymay add to the existing model, but groups that have no need to maintaincompatibility with such so-called legacy systems nearly always choosethe relational model for their databases.
The first databases to see wide use were large organizational databases thattoday would be called enterprise databases, built according to either thehierarchical model or the network model.
Systems built according to therelational model followed several years later.
SQL is a strictly modernlanguage; it applies only to the relational model and its descendant, theobject-relational model. Relational modelDr. Codd of IBM first formulated the relational database model in ,and this model started appearing in products about a decade later. That distinction went to a smallstart-up company, which named its product Oracle. Relational databases have almost completely replaced earlier database types. Suppose, for example, that you add one or more new columns toa database table.
Of course, if you remove a column that an existing application has to use, youexperience problems no matter what database model you follow. Why relational is betterIn applications written with DBMSs that follow the hierarchical or networkmodel, database structure is hard-coded into the application. That is, thewww. If you add a new attribute to the database, you must change yourapplication to accommodate the change, whether or not the applicationuses the new attribute.
An unmodified application will expect the data tobe arranged according to the old layout, so it will produce garbage when itwrites data into the file that now contains the new attribute. Relational databases offer structural flexibility; applications written forthose databases are easier to maintain than similar applications written forhierarchical or network databases.
Components of a relational databaseRelational databases gain their flexibility because their data resides in tablesthat are largely independent of each other.
You can add, delete, or changedata in a table without affecting the data in the other tables, provided thatthe affected table is not a parent of any of the other tables. In this section, I show what these tablesconsist of and how they relate to the other parts of a relational database.
Dealing with your relationsAt holiday time, many of my relatives come to my house and sit down at mytable. Databases have relations, too, but each of their relations has its owntable. A relational database is made up of one or more relations. A relation is a two-dimensional array of rows and columns, containing singlevaluedentries and no duplicate rows.
Each cell in the array can have only onevalue, and no two rows may be identical. Most people are familiar with two-dimensional arrays of rows and columns,in the form of electronic spreadsheets such as Microsoft Excel.
On the baseball card are columns forwww. A row coverseach year that the player has played in the Major Leagues. You can also storethis data in a relation a table , which has the same basic structure.
Figure shows a relational database table holding the offensive statistics for asingle major-league player. In practice, such a table would hold the statisticsfor an entire team — or perhaps the whole league.
The order in which the rowsand columns appear in the array has no significance.
The same is true of rows. The DBMS processes the table the same wayregardless of the organization. Every column in a database table embodies a single attribute of the table,just like that baseball card.
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