32 lines
1.1 KiB
PHP
32 lines
1.1 KiB
PHP
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Syntax: <br \>
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<div class='sql'>
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<pre>
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FROM <i>component_reference</i> [[LEFT | INNER] JOIN <i>component_reference</i>] ...
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</pre>
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</div>
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The FROM clause indicates the component or components from which to retrieve records.
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If you name more than one component, you are performing a join.
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For each table specified, you can optionally specify an alias.
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<br \><br \>
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<li \> The default join type is <i>LEFT JOIN</i>. This join can be indicated by the use of either 'LEFT JOIN' clause or simply ',', hence the following queries are equal:
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<div class='sql'>
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<pre>
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SELECT u.*, p.* FROM User u LEFT JOIN u.Phonenumber
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SELECT u.*, p.* FROM User u, u.Phonenumber p
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</pre>
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</div>
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<li \><i>INNER JOIN</i> produces a Cartesian product between two specified components (that is, each and every record in the first component is joined to each and every record in the second component).
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So basically <i>INNER JOIN</i> can be used when you want to efficiently fetch for example all users which have one or more phonenumbers.
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<div class='sql'>
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<pre>
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SELECT u.*, p.* FROM User u INNER JOIN u.Phonenumber p
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</pre>
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</div>
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