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Selecting Data Using Queries in Microsoft Access 2013

Resolving ambiguous outer joins

When you join tables together on a query and you have a line without any arrows at either end, you have an equally matched join (sometimes called an INNER JOIN or simply a JOIN). In the earlier parts of this section, we displayed unmatched records and missing parent records by adding an arrow at one end of the join; this is called an OUTER JOIN (being LEFT or RIGHT depending on which end all records are being displayed from). If you add tables to a query where you have already specified OUTER JOINS in the relationships, these will be shown by default when you add the tables to the query grid.

If you have a mixture of join types when you try to run a query, you will be warned that you have a join ambiguity, as shown here.