Visual Foxpro中数据库链接实验与研究

The Experiment and Research of Database Link Order in Visual Foxpro

在VF教学中发现使用数据库链接向导建立的查询或视图,由于链接数据表操作的顺序不同,而结果不同。经实验发现是由于查询语言的变化而导致结果的差异,经分析,VF中数据库链接顺序可分为直线型、汇聚型、分散型、反插型、环型,只有前两种是正确的链接方式。

In my Foxpro teaching I found that the query or viewgraph result was changing from the sorder of database link in using wizard. After experiment I found the reason was SQL language. The language＇ s mistake causeed the wrong result. The databse link sorder can be divided into 5 models： straight line type, convergent type, inserted type , dispersal type and toroidal type. Only straight llne type and convergent type are correct.