90 lines
5.9 KiB
HTML
90 lines
5.9 KiB
HTML
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<meta name="DC.Title" content="Process SELECT statements in a DB2 UDB CLI application" />
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<meta name="DC.subject" content="SQL, statements, SELECT" />
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<link rel="stylesheet" type="text/css" href="./ic.css" />
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<title>Process SELECT statements in a DB2 UDB CLI application</title>
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</head>
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<body id="rzadpprocsel"><a name="rzadpprocsel"><!-- --></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">Process SELECT statements in a DB2<sup>®</sup> UDB CLI application</h1>
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<div><div class="p">If the statement is a SELECT, the following steps are generally needed
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to retrieve each row of the result set: <ol><li>Establish the structure of the result set, number of columns, column types
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and lengths.</li>
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<li>Bind application variables to columns in
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order to receive the data.</li>
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<li>Repeatedly fetch the next row of data, and receive it into the bound application
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variables.<p>Columns that were not previously bound can be retrieved by calling <samp class="codeph">SQLGetData()</samp> after
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each successful fetch.</p>
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</li>
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</ol>
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</div>
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<div class="note"><span class="notetitle">Note:</span> Each of the above steps requires some diagnostic checks.</div>
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<div class="p">The first step requires analyzing the processed or prepared statement.
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If the SQL statement is generated by the application, this step is not necessary.
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This is because the application knows the structure of the result set and
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the data types of each column. If the SQL statement is generated (for example,
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entered by a user) at run time, the application needs to query:
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<ul><li>The number of columns</li>
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<li>The type of each column</li>
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<li>The names of each column in the result set.</li>
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</ul>
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This information can be obtained by calling <samp class="codeph">SQLNumResultCols()</samp> and <samp class="codeph">SQLDescribeCol()</samp> (or <samp class="codeph">SQLColAttributes()</samp>) after preparing the statement or after executing the statement.</div>
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<p>The second step allows
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the application to retrieve column data directly into an application variable
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on the next call to <samp class="codeph">SQLFetch()</samp>. For each column to be retrieved,
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the application calls <samp class="codeph">SQLBindCol()</samp> to bind an application
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variable to a column in the result set. Similar to variables bound to parameter
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markers using <samp class="codeph">SQLSetParam()</samp>, columns are bound using deferred
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arguments. This time the variables are output arguments, and data is written
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to them when <samp class="codeph">SQLFetch()</samp> is called. <samp class="codeph">SQLGetData()</samp> can
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also be used to retrieve data, so calling <samp class="codeph">SQLBindCol()</samp> is
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optional.</p>
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<p>The third step is to call <samp class="codeph">SQLFetch()</samp> to fetch the first
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or next row of the result set. If any columns have been bound, the application
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variable is updated. If any data conversion is indicated by the data types
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specified on the call to <samp class="codeph">SQLBindCol</samp>, the conversion occurs
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when <samp class="codeph">SQLFetch()</samp> is called. </p>
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<p>The last (optional) step, is to call <samp class="codeph">SQLGetData()</samp> to retrieve
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any columns that were not previously bound. All columns can be retrieved this
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way, provided they were not bound, or a combination of both methods can be
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used. <samp class="codeph">SQLGetData()</samp> is also useful for retrieving variable
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length columns in smaller pieces, which cannot be done with bound columns.
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Data conversion can also be indicated here, as in <samp class="codeph">SQLBindCol()</samp>. </p>
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<div class="p">For more information and examples refer to: <ul><li><a href="rzadphddtdcn.htm#rzadphddtdcn">Data types and data conversion in DB2 UDB CLI functions</a></li>
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<li><a href="rzadpfnbindc.htm#rzadpfnbindc">SQLBindCol - Bind a column to an application variable</a></li>
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<li><a href="rzadpfncolat.htm#rzadpfncolat">SQLColAttributes - Obtain column attributes</a></li>
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<li><a href="rzadpfndecol.htm#rzadpfndecol">SQLDescribeCol - Describe column attributes</a></li>
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<li><a href="rzadpfnfetch.htm#rzadpfnfetch">SQLFetch - Fetch next row</a></li>
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<li><a href="rzadpfngdata.htm#rzadpfngdata">SQLGetData - Get data from a column</a></li>
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<li><a href="rzadpfnnrcol.htm#rzadpfnnrcol">SQLNumResultCols - Get number of result columns</a></li>
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</ul>
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</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="rzadpprocessresults.htm">Processing results in a DB2 UDB CLI application</a></div>
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</div>
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</div>
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</body>
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</html>
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