108 lines
7.1 KiB
HTML
108 lines
7.1 KiB
HTML
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<title>Specify a search condition using the WHERE clause</title>
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<body id="rbafywhere"><a name="rbafywhere"><!-- --></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">Specify a search condition using the WHERE clause</h1>
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<div><p>The WHERE clause specifies a search condition that identifies the
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row or rows you want to retrieve, update, or delete.</p>
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<div class="section"><p>The number of rows you process with an SQL statement then depends
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on the number of rows that satisfy the WHERE clause <strong>search condition</strong>.
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A search condition consists of one or more <strong>predicates</strong>. A predicate
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specifies a test that you want SQL to apply to a specified row or rows of
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a table. </p>
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</div>
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<div class="section"><p>In the following example, WORKDEPT = 'C01' is a predicate, WORKDEPT
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and 'C01' are expressions, and the equal sign (=) is a comparison operator.
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Note that character values are enclosed in apostrophes (<samp class="codeph">'</samp>);
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numeric values are not. This applies to all constant values wherever they
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are coded within an SQL statement. For example, to specify that you are interested
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in the rows where the department number is C01, issue the following statement:</p>
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<pre>… <strong>WHERE</strong> WORKDEPT = 'C01'</pre>
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<p>In
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this case, the search condition consists of one predicate: WORKDEPT = 'C01'.</p>
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</div>
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<div class="section"><p>To further illustrate WHERE, put it into a SELECT statement. Assume
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that each department listed in the CORPDATA.DEPARTMENT table has a unique
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department number. You want to retrieve the department name and manager number
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from the CORPDATA.DEPARTMENT table for department C01. Issue the following
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statement: </p>
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<pre><strong>SELECT</strong> DEPTNAME, MGRNO
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<strong>FROM</strong> CORPDATA.DEPARTMENT
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<strong>WHERE</strong> DEPTNO = 'C01'</pre>
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</div>
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<div class="section"><p>When this statement is run, the result is one row: </p>
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<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" frame="hsides" border="1" rules="all"><caption>Table 1. Result table</caption><thead align="left"><tr><th valign="top" id="d0e79">DEPTNAME</th>
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<th valign="top" id="d0e81">MGRNO</th>
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</tr>
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</thead>
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<tbody><tr><td valign="top" headers="d0e79 ">INFORMATION CENTER</td>
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<td valign="top" headers="d0e81 ">000030</td>
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</tr>
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</tbody>
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</table>
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</div>
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</div>
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<div class="section"><p>If the search condition contains character, or UCS-2 or UTF-16
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graphic column predicates, the sort sequence that is in effect when the query
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is run is applied to those predicates. If a sort sequence is not being used,
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character constants must be specified in uppercase or lowercase to match the
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column or expression they are being compared to.</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="rbafywhereexp.htm">Expressions in the WHERE clause</a></strong><br />
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An expression in a WHERE clause names or specifies something you want to compare to something else.</li>
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<li class="ulchildlink"><strong><a href="rbafycompop.htm">Comparison operators</a></strong><br />
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SQL supports these comparison operators.</li>
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<li class="ulchildlink"><strong><a href="rbafynotkwd.htm">NOT keyword</a></strong><br />
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You can precede a predicate with the NOT keyword to specify that you want the opposite of the predicate's value (that is, TRUE if the predicate is FALSE, or vice versa).</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="rbafytexas.htm" title="Learn a variety of ways of tailoring your query to gather data using the SELECT statement. One way to do this is to use the SELECT statement in a program to retrieve a specific row (for example, the row for an employee). Furthermore, you can use clauses to gather data in a specific way.">Retrieve data using the SELECT statement</a></div>
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</div>
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<div class="relconcepts"><strong>Related concepts</strong><br />
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<div><a href="rbafyussisql.htm" title="A sort sequence defines how characters in a character set relate to each other when they are compared or ordered. Normalization allows you to compare strings that contain combining characters.">Sort sequences and normalization in SQL</a></div>
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</div>
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<div class="relref"><strong>Related reference</strong><br />
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<div><a href="rbafycomsrch.htm" title="In addition to the basic comparison predicates (=, >, <, and so on), a search condition can contain any of the predicates BETWEEN, IN, EXISTS, IS NULL, and LIKE.">Define complex search conditions</a></div>
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<div><a href="rbafymultiplewhere.htm" title="You can qualify your request further by coding a search condition that includes several predicates.">Multiple search conditions within a WHERE clause</a></div>
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