101 lines
6.6 KiB
HTML
101 lines
6.6 KiB
HTML
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<meta name="DC.Title" content="Bind an application" />
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<meta name="abstract" content="Before you can run your application program, a relationship between the program and any referred-to tables and views must be established. This process is called binding." />
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<meta name="DC.subject" content="application program, binding, binding an application, access plan, definition, SQL package, SQL package" />
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<title>Bind an application</title>
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</head>
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<body id="rbal1bind"><a name="rbal1bind"><!-- --></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">Bind an application</h1>
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<div><p>Before you can run your application program, a relationship between
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the program and any referred-to tables and views must be established. This
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process is called <dfn class="term">binding</dfn>.</p>
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<div class="section"><p>The result of binding is an access plan. The <dfn class="term">access plan</dfn> is
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a control structure that describes the actions necessary to satisfy each SQL
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request. An access plan contains information about the program and about the
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data the program intends to use. For distributed relational database work,
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the access plan is stored in the SQL package and managed by the server along
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with the SQL package.</p>
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</div>
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<div class="section"><p>SQL automatically attempts to bind and create access plans when
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the result of a successful compile is a program or service program object.
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If the compile is not successful or the result of a compile is a module object,
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access plans are not created. If, at run time, the database manager detects
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that an access plan is not valid or that changes have occurred to the database
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that might improve performance (for example, the addition of indexes), a new
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access plan is automatically created. If the application server (AS) is not
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an <span class="keyword">iSeries™ server</span>, then a bind must
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be done again using the <span class="cmdname">Create Structured Query Language Package
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(CRTSQLPKG)</span> command. binding does three things:</p>
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<ul><li>Revalidates the SQL statements using the description in the
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database. <p>During the bind process, the SQL statements are checked for
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valid table, view, and column names. If a referred to table or view does not
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exist at the time of the precompile or compile, the validation is done at
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run time. If the table or view does not exist at run time, a negative SQLCODE
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is returned.</p>
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</li>
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<li>Selects the access paths needed to access the data your program wants
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to process. <p>In selecting an access path, indexes, table sizes, and other
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factors are considered when SQL builds an access plan. The bind process considers
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all indexes available to access the data and decides which ones (if any) to
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use when selecting a path to the data.</p>
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</li>
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<li>Attempts to build access plans. <p>If all the SQL statements are valid,
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the bind process builds and stores access plans in the program.</p>
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</li>
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</ul>
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</div>
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<div class="section"><p>If the characteristics of a table or view your program accesses
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have changed, the access plan might no longer be valid. When you attempt to
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use an access plan that is not valid, the server automatically attempts to
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rebuild the access plan. If the access plan cannot be rebuilt, a negative
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SQLCODE is returned. In this case, you might have to change the program's
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SQL statements and reissue the CRTSQL<em>xxx</em> command to correct the situation.</p>
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</div>
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<div class="section"><p>For example, if a program contains an SQL statement that refers
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to COLUMNA in TABLEA and the user deletes and recreates TABLEA so that COLUMNA
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no longer exists, when you call the program, the automatic rebind is unsuccessful
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because COLUMNA no longer exists. You must change the program source and reissue
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the CRTSQL<em>xxx</em> command.</p>
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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="rbal1pdrdp.htm" title="When you write a program using SQL, you can embed the SQL statements in a host program.">Prepare distributed relational database programs</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="rbal1wrkpkg.htm" title="An SQL package is an SQL object used specifically by distributed relational database applications. It contains control structures for each SQL statement that accesses data on an application server (AS).">Work with SQL packages</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="rbal1packcreation.htm" title="An object called an SQL package can be created as part of the precompile process when the CRTSQLxxx command is compiled.">SQL package creation</a></div>
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<div><a href="../cl/crtsqlpkg.htm">Create Structured Query Language Package (CRTSQLPKG) command</a></div>
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</div>
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</div>
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</body>
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