105 lines
6.2 KiB
HTML
105 lines
6.2 KiB
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<title>Preparation and processing tasks in a DB2 UDB CLI application</title>
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<body id="rzadpprepexec"><a name="rzadpprepexec"><!-- --></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">Preparation and processing tasks in a DB2 UDB CLI application</h1>
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<div><div class="p">As soon as a statement handle has been allocated, there are two methods
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of specifying and executing SQL statements: <ol><li>Prepare, and then execute: <ol type="a"><li>Call <samp class="codeph">SQLPrepare()</samp> with an SQL statement as an argument.</li>
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<li>Call <samp class="codeph">SQLSetParam()</samp>, if the SQL statement contains <em>parameter
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markers</em>.</li>
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<li>Call <samp class="codeph">SQLExecute()</samp></li>
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</ol>
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</li>
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<li>Execute direct: <ol type="a"><li>Call <samp class="codeph">SQLSetParam()</samp>, if the SQL statement contains <em>parameter
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markers</em>.</li>
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<li>Call <samp class="codeph">SQLExecDirect()</samp> with an SQL statement as an argument.</li>
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</ol>
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</li>
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</ol>
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</div>
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<div class="p">The first method splits the preparation of the statement from the processing.
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This method is used when: <ul><li>The statement is processed repeatedly (typically with different parameter
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values). This avoids having to prepare the same statement more than once.</li>
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<li>The application requires information about the columns in the result set,
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before statement processing.</li>
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</ul>
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</div>
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<div class="p">The second method combines the preparation step and the processing step
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into one. This method is used when: <ul><li>The statement is processed once. This avoids having to call two functions
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to process the statement.</li>
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<li>The application does not require information about the columns in the
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result set, before the statement is processed.</li>
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</ul>
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</div>
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<p><strong>Binding parameters in SQL statements in a DB2<sup>®</sup> UDB CLI application</strong></p>
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<p>Both processing methods allow the use of parameter markers in place of
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an <em>expression</em> (or host variable in embedded SQL) in an SQL statement.</p>
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<p>Parameter markers are represented
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by the '?' character and indicate the position in the SQL statement where
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the contents of application variables are to be substituted when the statement
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is processed. The markers are referenced sequentially, from left to right,
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starting at 1.</p>
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<div class="p">When an application variable is
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associated with a parameter marker, it is <em>bound</em> to the
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parameter marker. Binding is carried out by calling the <samp class="codeph">SQLSetParam()</samp> function
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with: <ul><li>The number of the parameter marker</li>
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<li>A pointer to the application variable</li>
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<li>The SQL type of the parameter</li>
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<li>The data type and length of the variable.</li>
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</ul>
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The application variable is called a <em>deferred</em> argument because
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only the pointer is passed when <samp class="codeph">SQLSetParam()</samp> is called.
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No data is read from the variable until the statement is processed. This applies
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to both buffer arguments and arguments that indicate the length of the data
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in the buffer. Deferred arguments allow the application to modify the contents
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of the bound parameter variables, and repeat the processing of the statement
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with the new values.</div>
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<p>When calling <samp class="codeph">SQLSetParam()</samp>, it is possible
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to bind a variable of a different type from that required by the SQL statement.
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In this case DB2 UDB
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CLI converts the contents of the bound variable to the correct type. For example,
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the SQL statement might require an integer value, but your application has
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a string representation of an integer. The string can be bound to the parameter,
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and DB2 UDB
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CLI converts the string to an integer when you process the statement.</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="rzadpfnprep.htm#rzadpfnprep">SQLPrepare - Prepare a statement</a></li>
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<li><a href="rzadpfnspara.htm#rzadpfnspara">SQLSetParam - Set parameter</a></li>
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<li><a href="rzadpfnexec.htm#rzadpfnexec">SQLExecute - Execute a statement</a></li>
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<li><a href="rzadpfnexecd.htm#rzadpfnexecd">SQLExecDirect - Execute a statement directly</a></li>
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</ul>
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</div>
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<p>If the SQL statement uses parameter markers instead of expressions (or
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host variables in embedded SQL), you must bind the application variable to
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the parameter marker.</p>
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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="rzadphdptran.htm" title="This topic shows a typical order of function calls in a DB2 UDB CLI application.">Transaction processing task 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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