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Delphi database relationships

Posted on 1998-04-13
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Last Modified: 2013-11-23
Hello all,

      I'd like to knom how to built 1 to 1, 1 to n, m to n relationships in delphi databases using paradox tables? Paradox allows duplicated keys? How?

                  Tanks in advance
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Question by:oberdan
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by:julio011597
ID: 1361483
Yes, Paradox tables allow duplicate keys as long as they belong to secondary indexes.

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itamar earned 100 total points
ID: 1361484
Hi oberdan,

To implement relations:

1 to 1 - ORDERS.CustNo -> CUSTOMERS.CustNo
             In CUSTOMERS, CustNo must be the primary key or a unique index, so the relation will be from 1 record to 1 record;

1 to n - ORDERS.OderNo -> ITEMS.OrderNo
            In ITEMS, OrderNo must be a SECONDARY index AND with the Unique check box             unchecked. (This answer your second question). It's a typical master/detail model.

m to n - Not only in Paradox, but in any relational model, you must convert this relation in a               separated table with 2 fields, one for each foreign key of the tables related.

I sugest you to take a look at the ORDERS and ITEMS tables of DBDEMOS alias of Delphi.
There are typical cases in it.

IHTH,
Itamar


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