What is a foreign key ?
- Thread starter obs
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Just to put it in proper perspective for those reading this thread and not understanding all of the answer...
In a table, the primary key (PK) is used to find records. It must be unique.
In a table, a foreign key is VERY OFTEN part of a relationship with another (different) table. A foreign key is used to find the matching record in that other table. You store the other record's PK in this table's FK field.
A foreign key is VERY OFTEN on the "many" side of a one//many relationship, and the key on the "one" side of that same relationship is usually the PK of the corresponding table. Therefore, while a PK absolutely MUST be unique, an FK might not be unique.
I said "VERY OFTEN" above because sometimes the FK isn't necessarily a participant in a formal Access relationship as displayed in the Relationships Window. But it is ALWAYS an indicator of the location of something else related to the current table.
One last thing: You can only have one PK in a table. You can, however, have many different FKs in the same table, one for each actual or implied relationship with another data source.
In a table, the primary key (PK) is used to find records. It must be unique.
In a table, a foreign key is VERY OFTEN part of a relationship with another (different) table. A foreign key is used to find the matching record in that other table. You store the other record's PK in this table's FK field.
A foreign key is VERY OFTEN on the "many" side of a one//many relationship, and the key on the "one" side of that same relationship is usually the PK of the corresponding table. Therefore, while a PK absolutely MUST be unique, an FK might not be unique.
I said "VERY OFTEN" above because sometimes the FK isn't necessarily a participant in a formal Access relationship as displayed in the Relationships Window. But it is ALWAYS an indicator of the location of something else related to the current table.
One last thing: You can only have one PK in a table. You can, however, have many different FKs in the same table, one for each actual or implied relationship with another data source.
