Linking on multiple fields

[Portal 6]

I'm working with the "Alpha Five Made Easy The Basics and More for V10" book, on page 53.
The exercise creates a set linking on three fields, between two tables. I am working in the Add Relation dialog window. The last of the three fields is Parent field>zip code - Child field>zip.

A message appears at the bottom of the dialog window stating:
"Parent and Child Keys are different Lengths: Parent is 42 characters, child is 50."

The book says click OK, but with the message appearing the OK button is inactive. I know linked field names don't have to be the same, but does their length. Tracking lengths of fields sounds rediculous, especially if their names don't have to match.

How do I get past this message and save this three field relation. Or did I miss something.

Thanks

[MikeC]

Re: Linking on multiple fields

John,
First, I do not have Susan's tutorial....but think about it regarding field lengths and what it is you are trying to accomplish. A linkage that is created between two tables HAS to be unique in order to be absolutely certain that records will correspond correctly between the two tables. If the fields are of different lengths then it is possible for them to be different. Even spaces at the beginning or end of a name makes it different.

So control the field length either by making certain the table structures are the same or with code (using say the left() function).

When you say

Tracking lengths of fields sounds rediculous, especially if their names don't have to match

I am just a bit confused to say the least.....
Why does tracking the lengths sound rediculous?
And if the fields are linking fields then they sure better have matching names!!! :)

[Portal 6]

Re: Linking on multiple fields

Mike,
Thanks for replying.
--Quote-- A linkage that is created between two tables HAS to be unique in order to be absolutely certain that records will correspond correctly between the two tables.

I understand that the fields used in the book are very poor choices to use as linking fields, and the book points this out, but the book is trying to give an example lesson of multi field linking.

--Quote--If the fields are of different lengths then it is possible for them to be different.

Agreed, but even fields of the same name and same length can hold different values. So can fields of different length hold the same value. The focus of the linking is on the value. Most fields are longer than the info being entered. Tables used for linking may not have all come from you or the same programmer, so the name might not be identical, but the data is, or is supposed to be. So if you can't control the field name how can you control the length specified by another programmer, one space more or less makes it different.

--Quote--Even spaces at the beginning or end of a name makes it different.

I would think that fields designated as linking fields would automatically have leading and trailing spaces trimmed. I'm think about all the people entering info, how easy to accidently put a leading or trailing space. Theoretically that would render the info useless in respect to linking.

--Quote--Why does tracking the lengths sound rediculous?

It is so simple to control the name, but if that can't even be done, how can one control the length. Tables used for linking may not have all come from you or the same programmer.

What I have learned in Alpha is that the field names for linked fields do not have to be the same. Please someone confirm this one way or the other, so I can correct my knowledge if necessary.

Thanks,

[MikeC]

Re: Linking on multiple fields

I prefer it this way rather than having Alpha not give me a choice on how to do things. The use of the function alltrim() is probably one of the most used in Alpha as it gives certainty that leading and trailing spaces do not enter the equation. If the difference between two pieces of data is just a leading/trailing space then those two data values are NOT the same....makes sense to me.

Controlling the length is again an easy matter...the use of the function left(your_field_name, 50_or whtever length_wanted) gives the uniformity that is needed for linking fields.

Field names do not have to be the same if you are comparing data.