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In working with non- equijoin relationship matches, you may have noticed one oddball operator in the little menu of match criteria. Most of them are familiar comparison operators ”but what about the last one, the one that looks like an X?
Cross products really make sense only by themselves , in single-match relationships. They have no effect at all if they're added into multi-match criteria sets. A cross product match condition is always true, so it can never further limit the potential matches of other criteria. Of course, if that makes your head spin, you can just take our word for it. NOTE Savvy users of previous versions of FileMaker may recognize that the cross product operator replaces the technique that used to be known as a "constant" or "always-true" relationship. In that technique, you had to define specific fields on either side that explicitly matched each other ( generally a pair of calculations that each evaluated to 1) and build a relationship between the two fields. FileMaker 7's cross products provide the same feature in a more integrated fashion. Well, that explains what a cross product relationship is, but not how you might want to use one. The cross product is the ultimate nonstructural relationship. After all, its purpose is to show all of something. These are generally used for a variety of user interface purposes. Sometimes you might want users to pick from a list of things, for example, and it's more pleasing to allow them to pick from a scrolling list in a portal than from a dropdown list or menu. Generally such techniques need to be coupled with some scripting to react to users' choices. |
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