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【正文】 to be able to back out a transaction if part of it fails. ?You want to be able to locate the data somewhere more secure than the Web server, which could be in a DMZ or outside the firewall altogether. ?You want to be able to access data such as user data or products quickly, even if there are thousands or millions of them.When you add these items to the shopping list, only a relational database will really do the job effectively.MySQL Many sites don39。s the catch? What are you not getting in MySQL that makes people turn to Oracle? Well, MySQL is a neat little package, but it is missing some things that would be nice to have in a perfect world. A major feature that MySQL does not offer is database consistency checking. You can use foreign key tags in your schema, but MySQL cheerfully ignores them. A lot of DB As I know would consider this a very bad thing.A foreign key constraint prevents you from creating inconsistent data. For example, let39。 CREATE TABLE PURCHASE ( USERID FOREIGN KEY USER(USERID), ITEM INTEGER, QUANTITY INTEGER)。s, if you created an entry in the PURCHASE table with a user ID of 3, there would have to already be a user ID of 3 in the USER table or an error would occur. Similarly, you couldn39。s account and enter a record into the shipping table so that you39。s say that the second part fails. You wouldn39。d want to roll back to the state before the transaction began.So, MySQL isn39。s still good enough for probably 90% of the emerce sites in the world, however. And version , which is in alpha as of this writing, addresses a number of these concerns, including rowlevel locking and transaction control.Putting Tomcat and MySQL TogetherCombining Tomcat and MySQL provides a powerful, reliable, and free platform that you can use to learn, develop, and deploy JSP applications. And, best of all, the code that you develop using this platform will run nicely using iPlanet and Oracle or WebSphere and SQL Server.As a learning tool the two together are almost reference implementations of their respective protocols (JSP and SQL). As a result, you won39。re getting up to speed. In addition, you can enjoy the knowledge that you are supporting the opensource software movement. Opensource software is code that is made freely available under one of several public licenses, frequently the GNU General Public License (GPL).FACTS AND FICTION ABOUT THE GPLThe GNU General Public License is probably one of the most misunderstood documents in existence,The basics break down to this:1. If you place a piece of software under the GPL, anyone is free to make a copyof it in either source or executable form and give it to anyone else.2. If you take a piece of software under the GPL and use it as a part of yourproduct, you can39。t use GPL software for mercial purposes. Nothing is farther from the truth. What you can39。re not selling the site itself to a third party as a product. (Consulting panies fall into a weird quasispace, but no one has gone after them for using GPL software to date.)Why is it good to support this movement? There are two sides to this answer: one technical and one political. Technically, it39。s proprietary solution. It39。s a free solution out there if they aren39。是狼就要練好牙，是羊就要練好腿。不奮斗就是每天都很容易，可一年一年越來(lái)越難。拼一個(gè)春夏秋冬！贏一個(gè)無(wú)悔人生！早安！—————獻(xiàn)給所有努力的人.學(xué)習(xí)參考
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