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What are outer joins?

April 26, 2017joins Outer

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What are outer joins?

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Outer joins are SQL constructs that enable you to return rows from one table when there are no matching rows in a table to which it is joined. Consider the following scenario: the master table DEPT contains rows for department 10 (ACCOUNTS), department 20 (RESEARCH) and department 40 (OPERATIONS) the detail table EMP contains rows for Clark (department 10), Smith (department 20) and Allen (a former employee of department 30, which no longer exists) Figure 9-10 Master and detail tables DEPT and EMP, where the rows returned are determined by the position of the outer join construct in the query Text description of the illustration joind1.gif The following examples use the schema in the above figure to illustrate how the position of the outer join determines the rows returned from a query.