Types of Embedded Joins

With the relational adapters, you can describe two or more related tables in a single Master File. This type of multi-table structure is called an embedded join. There are two types of embedded joins:

In an embedded equijoin, each participating table must have at least one field in common with at least one other table in the structure. Typically, this common field is the primary key of one table and the foreign key of the other. A single Master and Access File pair can relate up to 1024 separate tables in this manner.

Multi-table Master and Access Files describe the relationships between tables. The adapter implements these relationships at run time by matching values in fields common to two or more tables for an equijoin, or by applying the specified conditions for a conditional join. A report or maintenance procedure can refer to any or all of the tables included in the multi-table description.

In this chapter, the terms primary key and foreign key refer to the common fields in two related tables. These may or may not have been described as primary and foreign keys in SQL CREATE TABLE statements (RDBMS referential integrity). In practice, FOCUS can use any two fields that share a common format to relate tables in multi-table file descriptions.

Note: This chapter describes manual methods for creating Master File and Access Files. Automated Procedures describes an automated method for creating Master and Access Files.


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