69 lines
4.8 KiB
HTML
69 lines
4.8 KiB
HTML
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<meta name="DC.Title" content="Inner join" />
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<meta name="abstract" content="An inner join returns only the rows from each table that have matching values in the join columns. Any rows that do not have a match between the tables will not appear in the result table." />
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<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
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<title>Inner join</title>
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<body id="rbafyinj"><a name="rbafyinj"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Inner join</h1>
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<div><p>An inner join returns only the rows from each table that have matching
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values in the join columns. Any rows that do not have a match between the
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tables will not appear in the result table.</p>
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<div class="section"><p>With an inner join, column values from one row of a table are
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combined with column values from another row of another (or the same) table
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to form a single row of data. SQL examines both tables specified for the join
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to retrieve data from all the rows that meet the search condition for the
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join. There are two ways of specifying an inner join: using the JOIN syntax,
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and using the WHERE clause.</p>
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</div>
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<div class="section"><p>Suppose you want to retrieve the employee numbers, names, and
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project numbers for all employees that are responsible for a project. In other
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words, you want the <em>EMPNO</em> and <em>LASTNAME</em> columns from the CORPDATA.EMPLOYEE
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table and the <em>PROJNO</em> column from the CORPDATA.PROJECT table. Only employees
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with last names starting with 'S' or later should be considered. To find this
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information, you need to join the two tables.</p>
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</div>
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</div>
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<div>
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<ul class="ullinks">
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<li class="ulchildlink"><strong><a href="rbafyinsyn.htm">Inner join using JOIN syntax</a></strong><br />
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To use the inner join syntax, both of the tables you are joining are listed in the FROM clause, along with the join condition that applies to the tables.</li>
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<li class="ulchildlink"><strong><a href="rbafyinwhere.htm">Inner join using the WHERE clause</a></strong><br />
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Using the WHERE clause to perform this same join as in the Inner join using JOIN syntax topic is written by entering both the join condition and the additional selection condition in the WHERE clause.</li>
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<li class="ulchildlink"><strong><a href="rbafyjoinusing.htm">Join data with the USING clause</a></strong><br />
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You can use a shorthand method of defining join conditions with the USING clause. The USING clause is equivalent to a join condition where each column from the left table is compared to a column with the same name in the right table.</li>
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</ul>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rbafyjoin.htm" title="Sometimes the information you want to see is not in a single table. To form a row of the result table, you might want to retrieve some column values from one table and some column values from another table. You can retrieve and join column values from two or more tables into a single row.">Join data from more than one table</a></div>
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</div>
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</div>
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</body>
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</html> |