HP 3000 Manuals HP 3000 Manuals
About Relations A relation specifies which records from the source tables are combined in the new table. Each relation consists of an item that is common to several source tables. The new, joined table consists of records in which the common item entries of all source tables have identical values. Relations can be thought of as filters which extract from all possible combinations only those records which match the relation (that is, have the same value). Relations need not affect all source tables. For example, if you joined four tables, you could define a relation that affects two, three, or all four tables. Whether or not you define a relation, you can use relation conditions (described in Chapter 6) to further restrict records written to a joined table. When you define a relation between two source tables, you are saying: "I want a record to be written to the joined table when item1 of table1 = item2 of table2."