ace said:
I did not intentially try to link two columns in the
same table! When and why would you do the self-join?
There are many instances when a self-join is necessary. One example is a
company's employee list, where each employee reports to a higher-level
employee. The record would contain a "foreign key" that refers to another
record (the one where the manager's information is stored). The top-level
person (the President/CEO/COO/Chairman) would not have a value in this
field. Another example would be a genealogy or pedigree list, where each
"child" has a foreign key to each of his/her parents.
I have a table_1 with no connections! Is that mean
a self-join?
No, it probably means that additional copy was erroneously added to the
Relationships. If someone else created this database, ask them if there
should be a self-join on some relationship; if you created it, just learn
from your mistake.
When there is a self-join, how do I find out which
columns were joined?
In the Relationships window, there will be a join line between the table and
the table_1, just as there is in any other relationship.
The same situation can occur in the Data Sources of a Query (the top portion
of the Query dialog) displayed in the Query Builder, and the same comments
apply. But, adding a table twice to a Query will not automatically create a
Relationship that will appear in the Relationships window.
Larry Linson
Microsoft Office Access MVP
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