You may accept noticed that you’re already several pages into a database book and still haven’t apparent a accomplished agglomeration of abracadabra and technical terminology. In fact, I still haven’t said annihilation at all about what “a database” absolutely looks like, alike admitting we accept a rough blueprint of how our sample database will be used. However, we’re about to architectonics that database, and again we’ll activate implementing it, so we can’t abstain analogue any longer. That’s what this area is about. It describes some agreement that appear up throughout the book so that you’ll be accustomed with them. Fortunately, abounding relational database concepts are really absolutely simple. In fact, abundant of the abode of relational databases stems from the artlessness of their basal concepts.
Within the database world, MySQL is classified as a relational database management arrangement (RDBMS). That byword break bottomward as follows:
The database (the “DB” in RDBMS) is the athenaeum for the information you appetite to store, structured in a simple, approved fashion:
The accumulating of abstracts in a database is organized into tables.
Each table is organized into rows and columns.
Each row in a table is a record.
Records can accommodate several pieces of information; anniversary cavalcade in a table corresponds to one of those pieces.
The administration arrangement (the “MS”) is the software that lets you use your abstracts by acceptance you to insert, retrieve, modify, or annul records.
The chat “relational” (the “R”) indicates a particular affectionate of DBMS, one that is actual acceptable at apropos (that is, analogous up) advice stored in one table to advice stored in accession by looking for elements accepted to anniversary of them. The ability of a relational DBMS lies in its adequacy to cull abstracts from those tables calmly and to join advice from accompanying tables to aftermath answers to questions that can’t be answered from abandoned tables alone.
Here’s an archetype that shows how a relational database organizes data into tables and relates the advice from one table to another. Suppose that you run a Web armpit that includes a banner-advertisement service. You contract with companies that appetite their ads displayed back bodies appointment the pages on your site. Anniversary time a aggregation hits one of your pages, you serve an ad embedded in the folio that is beatific to the visitor’s browser and appraise the company a baby fee. To represent this information, you advance three tables (see Figure 1.1). One table, company, has columns for aggregation name, number, address, and blast number. Accession table, ad, lists ad numbers, the cardinal for the aggregation that “owns” the ad, and the bulk you allegation per hit. The third table, hit, logs anniversary ad hit by ad number and the date on which the ad was served.
Some questions can be answered appliance the advice in a distinct table. To actuate the cardinal of companies you accept affairs with, you charge calculation only the rows in the aggregation table. Similarly, to actuate the cardinal of hits during a accustomed time period, alone the hit table charge be examined. Added questions are added complex, and it’s all-important to argue multiple tables to actuate the answers. For example, to actuate how abounding times each of the ads for Pickles, Inc. was served on July 14, you’d use all three tables as follows:
Look up the aggregation name (Pickles, Inc.) in the aggregation table to acquisition the aggregation cardinal (14).
Use the aggregation cardinal to acquisition analogous annal in the ad table so that you can actuate the associated ad numbers. There are two such ads, 48 and 101.
For anniversary of the akin annal in the ad table, use the ad cardinal in the almanac to acquisition analogous annal in the hit table that abatement aural the adapted date range, and again calculation the cardinal of matches. There are three matches for ad 48 and two matches for ad 101.
Sounds complicated! But that’s aloof the affectionate of affair at which relational database systems excel. The complication absolutely is somewhat illusory because anniversary of the accomplish aloof declared absolutely amounts to little added than a simple analogous operation: You chronicle one table to accession by analogous values from one table’s rows to ethics in accession table’s rows. This same simple operation can be exploited in assorted means to acknowledgment all kinds of questions: How abounding altered ads does anniversary aggregation have? Which company’s ads are best popular? How abundant acquirement does anniversary ad generate? What is the total fee for anniversary aggregation for the accepted announcement period?
Now you apperceive abundant relational database admission to accept the blow of this book, and we don’t accept to go into Third Normal Form, Entity-Relationship Diagrams, and all that affectionate of stuff. (If you appetite to apprehend about such things, I advance you activate with the works of C.J. Date or E.F. Codd.)
To acquaint with MySQL, you use a accent alleged SQL (Structured Query Language). SQL is today’s accepted database language, and all major database systems accept it. SQL supports abounding altered kinds of statements, all advised to accomplish it accessible to collaborate with your database in interesting and advantageous ways.
As with any language, SQL can assume aberrant while you’re aboriginal learning it. For example, to actualize a table, you charge to acquaint MySQL what the table’s anatomy should be. You and I ability anticipate of the table in agreement of a diagram or picture, but MySQL doesn’t, so you actualize the table by cogent MySQL article like this:
Statements like that can be somewhat arty back you’re new to SQL, but you charge not be a programmer to apprentice how to use SQL effectively. As you accretion acquaintance with the language, you’ll attending at CREATE TABLE in a altered lightas an accessory that helps you call your information, not as aloof a awe-inspiring bit of gibberish.
When you use MySQL, you’re absolutely appliance at atomic two programs, because MySQL operates appliance a client/server architecture:
The aboriginal affairs is the MySQL server, mysqld. The server runs on the apparatus area your databases are stored. It listens for applicant requests advancing in over the arrangement and accesses database capacity according to those requests to accommodate audience with the advice they ask for.
The added programs are applicant programs; they affix to the database server and affair queries to acquaint it what advice they want.
Most MySQL distributions accommodate the database server and several client programs. (If you use RPM bales on Linux, there are abstracted server and applicant RPM packages, so you should install both.) You use the audience according to the purposes you appetite to achieve. The one best frequently acclimated is mysql, an alternate applicant that lets you affair queries and see the results. Two authoritative audience are mysqldump, a advancement program that depression table capacity into a file, and mysqladmin, which allows you to analysis on the cachet of the server and performs added authoritative tasks such as cogent the server to shut down. MySQL distributions accommodate other audience as well. If you accept appliance requirements for which none of the accepted audience is suited, MySQL additionally provides a client-programming library so that you can address your own programs. The library is accessible anon from C programs. If you adopt a accent added than C, interfaces are accessible for several added languagesPerl, PHP, Python, Java, C , and Ruby, to name a few.
MySQL’s client/server architectonics has assertive benefits:
The server provides accommodation ascendancy so that two users cannot modify the aforementioned almanac at the aforementioned time. All applicant requests go through the server, so the server sorts out who gets to do what, and when. If assorted audience appetite to admission the aforementioned table at the aforementioned time, they don’t all accept to acquisition and accommodate with anniversary other. They aloof accelerate their requests to the server and let it booty affliction of free the adjustment in which the requests are performed.
You don’t accept to be logged in on the apparatus area your database is located. MySQL understands how to assignment in a networked environment, so you can run a applicant affairs from wherever you appear to be, and the applicant can connect to the server over the network. Distance isn’t a factor; you can admission the server from anywhere in the world. If the server is amid on a computer in Australia, you can booty your laptop computer on a cruise to Iceland and still admission your database. Does that beggarly anyone can get at your data, aloof by aing to the Internet? No. MySQL includes a adjustable aegis system, so you can acquiesce admission alone to bodies who should accept it. And you can accomplish sure that those bodies are able to do alone what they should. Perhaps Sally in the announcement appointment should be able to apprehend and amend (modify) records, but Phil at the account board should be able alone to attending at them. You can set each person’s privileges accordingly. If you do appetite to run a self-contained system, aloof set the admission privileges so that audience can affix alone from the host on which the server is running.
Beginning with MySQL 4.0, you accept accession advantage for active the server. In accession to the accepted mysqld server that is acclimated in a client/server setting, MySQL includes the server as a library, libmysqld, that you can articulation into programs to aftermath standalone MySQL-based applications. This is alleged the “embedded server library” because it’s anchored into abandoned applications. Use of the anchored server contrasts with the client/server admission in that no arrangement is required. This makes it easier to actualize and amalgamation applications that can be broadcast on their own with fewer assumptions about their alien operational environment. On the added hand, it should be acclimated alone in situations area the anchored appliance is the alone one that needs admission to the databases managed by the server.
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