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39 lines
1.2 KiB
Plaintext
39 lines
1.2 KiB
Plaintext
--------------
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New JOIN types
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--------------
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Author:
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Adriano dos Santos Fernandes <adrianosf@uol.com.br>
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Format:
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<named columns join> ::=
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<table reference> <join type> JOIN <table reference> USING ( <column list> )
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<natural join> ::=
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<table reference> NATURAL <join type> JOIN <table primary>
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Notes:
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Named columns join:
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1) All columns specified in <column list> should exist in the tables of both sides.
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2) An equi-join (<left table>.<column> = <right table>.<column>) is automatically
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created for all columns (ANDed).
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3) The USING columns can be accessed without qualifier, and in this case, result of
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it is COALESCE(<left table>.<column>, <right table>.<column>).
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4) In "SELECT *", USING columns are expanded once, using the above rule.
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Natural join:
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1) A "named columns join" is automatically created with all columns common to the
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left and right tables.
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2) If the is no common column, a CROSS JOIN is created.
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Examples:
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1) select *
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from employee
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join department
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using (dept_no);
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2) select *
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from employee_project
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natural join employee
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natural join project;
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