120 lines
7.9 KiB
HTML
120 lines
7.9 KiB
HTML
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<title>Multiple search conditions within a WHERE clause</title>
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<body id="rbafymultiplewhere"><a name="rbafymultiplewhere"><!-- --></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">Multiple search conditions within a WHERE clause</h1>
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<div><p>You can qualify your request further by coding a search condition
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that includes several predicates.</p>
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<div class="section"><p>The search condition you specify can contain any of the comparison
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operators or the predicates BETWEEN, DISTINCT, IN, LIKE, EXISTS, IS NULL,
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and IS NOT NULL.</p>
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</div>
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<div class="section"><p>You can combine any two predicates with AND and OR. In addition,
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you can use the NOT keyword to specify that the search condition that you
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want is the negated value of the specified search condition. A WHERE clause
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can have as many predicates as you want.</p>
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<ul><li><strong>AND</strong> says that, for a row to qualify, the row must satisfy both
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predicates of the search condition. For example, to find out which employees
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in department D21 were hired after December 31, 1987, specify: <pre>…
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<strong>WHERE</strong> WORKDEPT = 'D21' <strong>AND</strong> HIREDATE > '1987-12-31'</pre>
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</li>
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<li><strong>OR</strong> says that, for a row to qualify, the row can satisfy the condition
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set by either or both predicates of the search condition. For example, to
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find out which employees are in either department C01 or D11, you can specify
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: <pre>…
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<strong>WHERE</strong> WORKDEPT = 'C01' <strong>OR</strong> WORKDEPT = 'D11'</pre>
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<div class="note"><span class="notetitle">Note:</span> You
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can also use IN to specify this request: WHERE WORKDEPT IN (<samp class="codeph">'</samp>C01<samp class="codeph">'</samp>, <samp class="codeph">'</samp>D11<samp class="codeph">'</samp>).</div>
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</li>
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<li><strong>NOT</strong> says that, to qualify, a row must not meet the criteria set
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by the search condition or predicate that follows the NOT. For example, to
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find all employees in department E11 except those with a job code equal to
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analyst, you can specify: <pre>…
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<strong>WHERE</strong> WORKDEPT = 'E11' <strong>AND NOT</strong> JOB = 'ANALYST'</pre>
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</li>
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</ul>
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</div>
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<div class="section"><p>When SQL evaluates search conditions that contain these connectors,
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it does so in a specific order. SQL first evaluates the NOT clauses, next
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evaluates the AND clauses, and then the OR clauses.</p>
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</div>
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<div class="section"><p>You can change the order of evaluation by using parentheses. The
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search conditions enclosed in parentheses are evaluated first. For example,
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to select all employees in departments E11 and E21 who have education levels
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greater than 12, you can specify: </p>
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<pre>…
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<strong>WHERE</strong> EDLEVEL > 12 <strong>AND</strong>
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(WORKDEPT = 'E11' <strong>OR</strong> WORKDEPT = 'E21')</pre>
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<p>The parentheses
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determine the meaning of the search condition. In this example, you want all
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rows that have a: </p>
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<ul><li>WORKDEPT value of E11 or E21, and</li>
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<li>EDLEVEL value greater than 12</li>
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</ul>
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</div>
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<div class="section"><p>If you did not use parentheses: </p>
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<pre>…
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<strong>WHERE</strong> EDLEVEL > 12 <strong>AND</strong> WORKDEPT = 'E11'
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<strong>OR</strong> WORKDEPT = 'E21'</pre>
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</div>
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<div class="section"><p>Your result is different. The selected rows are rows that have:
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</p>
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<ul><li>WORKDEPT = E11 and EDLEVEL > 12, or</li>
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<li>WORKDEPT = E21, regardless of the EDLEVEL value</li>
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</ul>
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</div>
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<div class="section"><img src="./delta.gif" alt="Start of change" /><p>If you are combining multiple equal comparisons,
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you can write the predicate with the ANDs as shown in the following example:</p>
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<pre>…
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<strong>WHERE</strong> WORKDEPT = 'E11' <strong>AND</strong> EDLEVEL = 12 <strong>AND</strong> JOB = 'CLERK'</pre>
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<p>You can also compare two lists, for example:</p>
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<pre>…
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<strong>WHERE</strong> (WORKDEPT, EDLEVEL, JOB) = ('E11', 12, 'CLERK')</pre>
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<p>When
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two lists are used, the first item in the first list is compared to the first
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item in the second list, and so on through both lists. Thus, each list must
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contain the same number of entries. Using lists is identical to writing the
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query with AND. Lists can only be used with the equal and not equal comparison
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operators.</p>
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<img src="./deltaend.gif" alt="End of change" /></div>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <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>
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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="rbafywhere.htm" title="The WHERE clause specifies a search condition that identifies the row or rows you want to retrieve, update, or delete.">Specify a search condition using the WHERE clause</a></div>
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</div>
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</div>
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