70 lines
2.4 KiB
PHP
70 lines
2.4 KiB
PHP
SELECT statement syntax:
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<div class='sql'>
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<pre>
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SELECT
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[ALL | DISTINCT]
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<i>select_expr</i>, ...
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[FROM <i>components</i>
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[WHERE <i>where_condition</i>]
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[GROUP BY <i>groupby_expr</i>
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[ASC | DESC], ... ]
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[HAVING <i>where_condition</i>]
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[ORDER BY <i>orderby_expr</i>
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[ASC | DESC], ...]
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[LIMIT <i>row_count</i> OFFSET <i>offset</i>}]
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</pre>
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</div>
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<br \>
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The SELECT statement is used for the retrieval of data from one or more components.
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<ul>
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<li \>Each <i>select_expr</i> indicates a column or an aggregate function value that you want to retrieve. There must be at least one <i>select_expr</i> in every SELECT statement.
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<div class='sql'>
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<pre>
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SELECT a.name, a.amount FROM Account a
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</pre>
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</div>
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<li \>An asterisk can be used for selecting all columns from given component. Even when using an asterisk the executed sql queries never actually use it
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(Doctrine converts asterisk to appropriate column names, hence leading to better performance on some databases).
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<div class='sql'>
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<pre>
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SELECT a.* FROM Account a
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</pre>
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</div>
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<li \>FROM clause <i>components</i> indicates the component or components from which to retrieve records.
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<div class='sql'>
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<pre>
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SELECT a.* FROM Account a
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SELECT u.*, p.*, g.* FROM User u LEFT JOIN u.Phonenumber p LEFT JOIN u.Group g
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</pre>
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</div>
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<li \>The WHERE clause, if given, indicates the condition or conditions that the records must satisfy to be selected. <i>where_condition</i> is an expression that evaluates to true for each row to be selected. The statement selects all rows if there is no WHERE clause.
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<div class='sql'>
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<pre>
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SELECT a.* FROM Account a WHERE a.amount > 2000
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</pre>
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</div>
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<li \>In the WHERE clause, you can use any of the functions and operators that DQL supports, except for aggregate (summary) functions
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<li \>The HAVING clause can be used for narrowing the results with aggregate functions
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<div class='sql'>
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<pre>
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SELECT u.* FROM User u LEFT JOIN u.Phonenumber p HAVING COUNT(p.id) > 3
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</pre>
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</div>
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<li \>The ORDER BY clause can be used for sorting the results
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<div class='sql'>
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<pre>
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SELECT u.* FROM User u ORDER BY u.name
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</pre>
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</div>
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<li \>The LIMIT and OFFSET clauses can be used for efficiently limiting the number of records to a given <i>row_count</i>
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<div class='sql'>
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<pre>
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SELECT u.* FROM User u LIMIT 20
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</pre>
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</div>
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</ul>
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