107 lines
6.1 KiB
HTML
107 lines
6.1 KiB
HTML
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<meta name="DC.Title" content="Indicator variables in applications that use SQL" />
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<meta name="abstract" content="An indicator variable is a halfword integer variable used to indicate whether its associated host variable has been assigned a null value." />
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<meta name="description" content="An indicator variable is a halfword integer variable used to indicate whether its associated host variable has been assigned a null value." />
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<title>Indicator variables in applications that use SQL</title>
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</head>
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<body id="rzajpindvar"><a name="rzajpindvar"><!-- --></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">Indicator variables in applications that use SQL</h1>
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<div><p>An <em>indicator variable</em> is a halfword integer variable used
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to indicate whether its associated host variable has been assigned a null
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value.</p>
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<div class="section"><ul><li>If the value for the result column is null, SQL puts a -1 in the indicator
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variable.</li>
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<li>If you do not use an indicator variable and the result column is a null
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value, a negative SQLCODE is returned.</li>
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<li>If the value for the result column causes a data mapping error. SQL sets
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the indicator variable to -2.</li>
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</ul>
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</div>
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<div class="section"><p>You can also use an indicator variable to verify that a retrieved
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string value has not been truncated. If truncation occurs, the indicator variable
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contains a positive integer that specifies the original length of the string.
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If the string represents a large object (LOB), and the original length of
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the string is greater than 32767, the value that is stored in the indicator
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variable is 32767, since no larger value can be stored in a halfword integer.</p>
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<p>When
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the database manager returns a value from a result column, you can test the
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indicator variable. If the value of the indicator variable is less than zero,
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you know the value of the results column is null. When the database manager
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returns a null value, the host variable will be set to the default value for
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the result column.</p>
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</div>
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<div class="section"><div class="p">You specify an indicator variable (preceded by a colon) immediately
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after the host variable or immediately after the keyword INDICATOR. For example: <pre>EXEC SQL
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<strong>SELECT COUNT</strong>(*), <strong>AVG</strong>(SALARY)
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<strong>INTO</strong> :PLICNT, :PLISAL:INDNULL
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<strong>FROM</strong> CORPDATA.EMPLOYEE
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<strong>WHERE</strong> EDLEVEL < 18
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END-EXEC.</pre>
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</div>
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</div>
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<div class="section"><p>You can then test INDNULL to see if it contains a negative value.
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If it does, you know SQL returned a null value.</p>
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</div>
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<div class="section"><p>Always test for NULL in a column by using the <strong><var class="varname">IS NULL</var></strong> predicate.
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For example:</p>
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<pre><strong>WHERE</strong> expression <strong>IS NULL</strong>
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</pre>
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</div>
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<div class="section"><p>Do not test for NULL in this way:</p>
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<pre><strong>MOVE</strong> -1 <strong>TO HUIND.</strong>
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EXEC SQL...<strong>WHERE</strong> column-name = :HUI :HUIND
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</pre>
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</div>
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<div class="section"><p>The EQUAL predicate will always be evaluated as false when it
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compares a null value. The result of this example will select
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no rows.</p>
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</div>
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<div class="section"><p>The DISTINCT predicate can be used to perform comparisons when
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null values may exist.</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="rzajphostindvar.htm">Indicator variables used with host structures</a></strong><br />
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You can also specify an <em>indicator structure</em> (defined
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as an array of halfword integer variables) to support a host structure.</li>
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<li class="ulchildlink"><strong><a href="rzajpnullvar.htm">Indicator variables used to set null values</a></strong><br />
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You can use an indicator variable to set a null value in a column.</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="rzajphostvar.htm" title="When your program retrieves data, the values are put into data items defined by your program and specified with the INTO clause of a SELECT INTO or FETCH statement. The data items are called host variables.">Use host variables in SQL statements</a></div>
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</div>
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<div class="relinfo"><strong>Related information</strong><br />
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<div><a href="../db2/rbafzmstch2pred.htm">Predicates</a></div>
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</div>
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</div>
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</body>
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