163 lines
11 KiB
HTML
163 lines
11 KiB
HTML
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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static SQL, defined, dynamic SQL, preparation and execution, static select,
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dynamic select, interactive entry of SQL statements" />
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<title>How SQL statements are invoked</title>
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<a id="Top_Of_Page" name="Top_Of_Page"></a><!-- Java sync-link -->
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<a name="howsql"></a>
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<h2 id="howsql"><a href="rbafzmst02.htm#ToC_722">How SQL statements are invoked</a></h2>
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<p><a id="idx1261" name="idx1261"></a><a id="idx1262" name="idx1262"></a></p>
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<p>The SQL statements described in this chapter are classified as <span class="italic">executable</span> or <span class="italic">nonexecutable</span>. The <span class="italic">Invocation</span> section in the description of each statement indicates whether
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or not the statement is executable.</p>
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<p>An <span class="italic">executable statement</span> can be invoked in any of
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the following ways: </p>
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<ul>
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<li>Embedded in an application program</li>
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<li>Dynamically prepared and executed</li>
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<li>Issued interactively</li></ul><p class="indatacontent"> </p>
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<a name="wq1020"></a>
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<div class="notetitle" id="wq1020">Note:</div>
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<div class="notebody">Statements embedded in REXX or processed using RUNSQLSTM
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are prepared and executed dynamically.</div>
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<p>Depending on the statement, you can use some or all of these methods. The <span class="italic">Invocation</span> section in the description of each statement
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tells you which methods can be used.</p>
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<p>A <span class="italic">nonexecutable statement</span> can only be embedded
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in an application program.</p><a id="idx1263" name="idx1263"></a><a id="idx1264" name="idx1264"></a>
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<a name="wq1021"></a>
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<h3 id="wq1021"><a href="rbafzmst02.htm#ToC_723">Embedding a statement in an application program</a></h3>
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<p>SQL statements can be included in a source program that will be submitted
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to the precompiler by using the CRTSQLCBL, CRTSQLCBLI, CRTSQLCI, CRTSQLFTN,
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CRTSQLCPPI, CRTSQLPLI, CRTSQLRPG, or CRTSQLRPGI commands. Such statements
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are said to be <span class="italic">embedded</span> in the program. An embedded
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statement can be placed anywhere in the program where a host language statement
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is allowed. Each embedded statement must be preceded by a keyword (or keywords)
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to indicate that the statement is an SQL statement:</p>
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<ul>
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<li>In C, COBOL, FORTRAN, PL/I, and RPG, each embedded statement must be preceded
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by the keywords EXEC and SQL.</li>
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<li>In Java™, each embedded statement must be preceded by the keywords #sql.</li>
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<li>In REXX, each embedded statement must be preceded by the keyword EXECSQL.</li></ul>
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<a name="wq1022"></a>
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<h4 id="wq1022">Executable statements</h4><a id="idx1265" name="idx1265"></a>
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<p>An executable statement embedded in an application program is executed
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every time a statement of the host language would be executed if specified
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in the same place. This means that a statement within a loop is executed every
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time the loop is executed, and a statement within a conditional construct
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is executed only when the condition is satisfied.</p>
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<p>An embedded statement can contain references to variables. A
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variable referenced in this way can be used in two ways: </p>
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<ul>
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<li>As input (the current value of the variable is used in the execution of
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the statement)</li>
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<li>As output (the variable is assigned a new value as a result of executing
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the statement)</li></ul><p class="indatacontent"> In particular, all references to variables in expressions and predicates
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are effectively replaced by current values of the variables; that is, the
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variables are used as input. The treatment of other references is described
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individually for each statement.</p>
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<p>All executable statements should be followed by a test of an SQL return
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code. Alternatively, the WHENEVER statement (which is itself nonexecutable)
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can be used to change the flow of control immediately after the execution
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of an embedded statement.</p>
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<p>Objects referenced in SQL statements need not exist when the statements
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are prepared.</p>
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<a name="wq1023"></a>
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<h4 id="wq1023">Nonexecutable statements</h4><a id="idx1266" name="idx1266"></a>
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<p>An embedded nonexecutable statement is processed only by the precompiler.
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The precompiler reports any errors encountered in such a statement. The statement
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is <span class="italic">never</span> executed, and acts as a no-operation if placed
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among executable statements of the application program. Therefore, do not
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follow such statements by a test of an SQL return code.</p>
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<a name="wq1024"></a>
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<h3 id="wq1024"><a href="rbafzmst02.htm#ToC_726">Dynamic preparation and execution</a></h3><a id="idx1267" name="idx1267"></a>
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<p>An application program can dynamically build an SQL statement in the form
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of a character string placed in a variable. In general, the statement is built
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from some data available to the program (for example, input from a workstation).
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The statement can be prepared for execution using the (embedded) statement
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PREPARE and executed by the (embedded) statement EXECUTE. Alternatively, the
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(embedded) statement EXECUTE IMMEDIATE can be used to prepare and execute
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a statement in one step. In Java, the statement can be prepared for
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execution by means of the Statement, PreparedStatement, and CallableStatement
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classes, and executed by means of their respective execute() methods.</p>
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<p>A statement that is dynamically prepared must not contain references to
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variables. It can contain parameter markers instead. See <a href="rbafzmstpreph2.htm#preph2">PREPARE</a> for
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rules concerning the parameter markers. When the prepared statement is executed,
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the parameter markers are effectively replaced by the current values of the
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variables specified in the EXECUTE statement. See <a href="rbafzmsthexeqt.htm#hexeqt">EXECUTE</a> for
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rules concerning this replacement. After a statement is prepared, it can be
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executed several times with different values of variables. Parameter markers
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are not allowed in EXECUTE IMMEDIATE.</p>
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<p>In C, COBOL, FORTRAN, PL/I, REXX, and RPG, the successful or unsuccessful
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execution of the statement is indicated by the values returned in the stand-alone
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SQLCODE or SQLSTATE after the EXECUTE (or EXECUTE IMMEDIATE) statement. The
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SQL return code should be checked as described above for embedded statements.
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See the topic <a href="rbafzmstcksql.htm#cksql">SQL return codes</a> for more information. In Java, the successful or unsuccessful execution of the statement is handled
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by Java Exceptions.</p>
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<a name="wq1025"></a>
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<h3 id="wq1025"><a href="rbafzmst02.htm#ToC_727">Static invocation of a select-statement</a></h3><a id="idx1268" name="idx1268"></a>
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<p>A <span class="italic">select-statement</span> can be included as a part of
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the (nonexecutable) statement DECLARE CURSOR. Such a statement is executed
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every time the cursor is opened by means of the (embedded) statement OPEN.
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After the cursor is open, the result table can be retrieved one row at a time
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by successive executions of the FETCH statement or multiple rows at a time
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by using the multiple-row FETCH statement.</p>
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<p>Used in this way, the <span class="italic">select-statement</span> can contain
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references to variables. These references are effectively replaced by the
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values that the variables have at the moment of executing OPEN.</p>
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<a name="wq1026"></a>
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<h3 id="wq1026"><a href="rbafzmst02.htm#ToC_728">Dynamic invocation of a select-statement</a></h3><a id="idx1269" name="idx1269"></a>
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<p>An application program can dynamically build a <span class="italic">select-statement</span> in the form of a character string placed in a variable. In general,
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the statement is built from some data available to the program (for example,
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a query obtained from a workstation). The statement is then executed every
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time the cursor is opened by means of the (embedded) statement OPEN. After
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the cursor is open, the result table can be retrieved one row at a time by
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successive executions of the FETCH statement or multiple rows at a time by
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using the multiple-row FETCH statement.</p>
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<p>Used in this way, the <span class="italic">select-statement</span> must not
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contain references to variables. It can instead contain parameter markers.
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See <a href="rbafzmstpreph2.htm#preph2">PREPARE</a> for rules concerning the parameter markers. The
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parameter markers are effectively replaced by the values of the variables
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specified in the OPEN statement. See <a href="rbafzmsthopen.htm#hopen">OPEN</a> for rules concerning
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this replacement.</p>
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<a name="wq1027"></a>
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<h3 id="wq1027"><a href="rbafzmst02.htm#ToC_729">Interactive invocation</a></h3><a id="idx1270" name="idx1270"></a>
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<p>A capability for entering SQL statements from a workstation is part of
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the architecture of the database manager. The DB2 UDB for iSeries licensed program provides
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the Start Structured Query Language (STRSQL) command, the Start Query Manager
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(STRQM) command, and the Run SQL Script support of iSeries Navigator for this facility.
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Other products are also available. A statement entered in this way is said
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to be issued interactively. A statement that cannot be dynamically prepared
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cannot be issued interactively, with the exception of connection management
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statements (CONNECT, DISCONNECT, RELEASE, and SET CONNECTION).</p>
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<p>A statement issued interactively must be an executable statement that does
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not contain parameter markers or references to variables, because these make
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sense only in the context of an application program.</p>
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<hr /><br />
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[ <a href="#Top_Of_Page">Top of Page</a> | <a href="rbafzmststates.htm">Previous Page</a> | <a href="rbafzmstcksql.htm">Next Page</a> | <a href="rbafzmst02.htm#wq1">Contents</a> |
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