Relationships

Type

Concept

Purpose

A Relationship is a link between two groups of records whether in the same table or in two different tables. When two groups of records are related, you can access information in one group while processing records in the other group. DataEase employs two types of relationships.

In a predefined relationship, the two groups of records are related by a link entered on a Relationships form. The link is created by specifying one or more fields that hold the same information in both groups. Because this relationship is stored in the database, it can be used in different procedures whenever necessary.

An ad hoc relationship is a relationship that is defined while creating a script. Although an ad hoc relationship can be used like a predefined relationship to access information in another group of records, the relationship isn't stored as a part of the database. Therefore, it can only be used in the procedure in which it is defined.

Usage

In a script, a value in a related table or group of records is called a relationship value. A relationship value can be used in a script wherever you can use a field, a constant value, or a variable (such as in selection criteria, as a list item, or as a value assigned to a temporary or global variable).

Once a relationship is established, the DQL Relational Operators let you access and manipulate values in the related table. For example, if the script is processing MEMBERS records, the statement:

 sum of RESERVATIONS TOTAL DUE ;

..sums the TOTAL DUE field for each related reservation (that is, for every RESERVATIONS record with the same MEMBER ID as the MEMBERS record currently being processed).

The use of each Relational Operator is covered in a separate entry in this Language Reference.