User manual

Chapter 4 | Working with related tables and files 87
Relational database terminology
Before you begin working with relational databases and lookups, you should understand the
following terms. These terms are explained in the sections that follow.
Term Description
Current table For relational databases, the table that you are currently working in.
For lookups, the table that the data is copied to.
External table A table outside of the current file, in another file.
Lookup target field
(for lookups only)
The field in a table that you want data copied to during a lookup.
Lookup source field
(for lookups only)
The field in the related table that contains the data you want copied during a lookup.
Match field A field in the current table and a field in a related table that each contains values used to
access matching records. (A match field is sometimes called a key field.) For each
relationship, you select one or more match fields in each table.
For relational databases, values in match fields must match each other in some way for a
relationship to be established between the files. See
“About match fields for relationships” on
page 88.
For lookups, values in match fields do not have to be equal to match.
Portal A layout object that displays records from related tables. Portals display data from related
fields in rows, one record in each row.
Related field A field in one table that is related to a field in another table (or to a different field within the
same table). If a relationship has been created between two tables (even through another
table), data in fields in one table can be accessed from the other table.
Related record A record in the related table whose match field (according to the relationship used) contains
a value that matches the value in the match field of another table.
Related table For relational databases, the table that contains the data you want to access and work with in
the current table.
For lookups, the table that contains the data to copy.
A table can be related to itself. This is called a self-join.
Relational
operators
In the relationships graph, the symbols that define the match criteria between one or more pairs
of fields in two tables. These include: equal (=), not equal (≠), greater than (>), greater than or
equal to (≥), less than (<), less than or equal to (≤), and all rows, or cartesian product (X).
Relationship Relationships provide access to data from one table to another. Relationships can join one
record in one table to one record in another table, one record to many other records, or all
records in one table to all records in another table, depending on the criteria you specify when
you create the relationship in the relationships graph. (A relationship is sometimes called a
link or a join expression.)
Relationships
graph
In the Relationships tab of the Manage Database dialog box, you can see the occurrences of
tables both in the current file and from any external, related database files. In this relationships
graph, you join tables and change relationships between fields in different tables.
When you create a new table, a visual representation, or occurrence, of the table appears in
the relationships graph. You can specify multiple occurrences (with unique names) of the
same table in order to work with complex relationships in the graph.
Source file The file from which you add a table to the relationships graph.
Source table The table upon which one or more tables in the relationships graph are based. The source
table is the table defined in the Tables tab of the Manage Database dialog box.