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Outer joins are used when you want the records on the one side of a one-to-many relationship to be included in the query result, regardless of whether there are matching records in the table on the many side. With a Customers table and an Orders table, for example, users often want to include only customers with orders in the query output. An inner join (the default join type) does this. In other situations, users want all customers to be included in the query result, regardless of whether they have orders. This is when an outer join is necessary.
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