Access入门教程 18.1 何时使用导入或联接
在Access中，可以很方便地从外部数据库中获取数据，这些数据库包括现在所有的各种主流数据库，像Dbase、 Sybase、Oracle、Foxpro等。这样你就不用去一个一个地重新输入原来的数据了。在Access中，可以用获取外部数据命令来获取外部数据库的数据，这个命令包
在Access中，可以很方便地从外部数据库中获取数据，这些数据库包括现在所有的各种主流数据库，像Dbase、 Sybase、Oracle、Foxpro等。这样你就不用去一个一个地重新输入原来的数据了。在Access中，可以用"获取外部数据"命令来获取外部数据库的数据，这个命令包括两种方式"导入"和"链接表".对于不同的外部数据库可以用不同的获取方式。而且在Access中，不光可以获取外部数据，还可以导出别的数据库，就是将用Access建立的数据库保存为别的数据库形式，像 FOXPRO,DBASE数据库等。
单击"文件"菜单中的"获取外部数据"项，弹出一个子菜单，上面有"导入"和"链接表"两个选项。我们单击其中的一个选项就可以实现导入或联接一个外部的数据库。虽然这两个命令的功用都是打开外部的一个数据库，并从中获取需要的数据，但在使用上，还是有差别的。
在我们使用"导入"这个方法来获取外部数据时需要注意几个条件。
一、需要我们打开的数据库文件相对来说比较小，而且不会被其他数据库应用程序的用 户频繁更改。
二、不需要与其他数据库应用程序的用户共享数据。
三、你正在替换以前的数据库应用程序，而且不再需要以前的数据格式。
四、在使用其他数据库中的数据时，需要最佳性能。
使用"链接表"方法来获取外部数据时也需要注意几个条件：
一、需要打开的文件比较大，甚至比本地Access数据库的最大容量（1GB）还要大。
二、这个文件经常被其他数据库应用程序的用户更改。
三、必须在网络上与其他数据库应用程序的用户共享这个文件。
四、需要把应用程序分布到几个单独的用户那里，而且，你可能要不断更新开发的应用程序接口，将"应用程序"与数据分开可以更容易地更新应用程序，而不会干扰用户积累的数据。
这就是为什么要在"获取外部数据"这个过程当中设置两种方法。如果要用的数据库并不大，但每天都可能要修改，而且由几个人来修改不同的部分，对于这种情况，最重要的是每天都有新的数据要处理，而单纯的将表导入进来，由于在Access中开发新的系统需要一定的时间，在这段时间内就有可能有新的数据输入进来。开始导入的数据就有很多可能已经更新了。所以这时使用"链接表"就不会出现这种问题，干扰到别的用户积累的数据。当然在Access中执行现在这台机器上的数据库文件是最快的，使用链接常常会因为很多原因使你的工作变得很慢，这点是你必须考虑的。
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