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<meta name="DC.Title" content="Explicit connection management" />
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<meta name="abstract" content="The CONNECT statement is used to explicitly connect an application requester (AR) to an identified application server (AS). This SQL statement can be embedded within an application program or you can issue it using Interactive SQL." />
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<title>Explicit connection management</title>
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<body id="rbal1excon"><a name="rbal1excon"><!-- --></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">Explicit connection management</h1>
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<div><p>The CONNECT statement is used to explicitly connect an application
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requester (AR) to an identified application server (AS). This SQL statement
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can be embedded within an application program or you can issue it using Interactive
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SQL.</p>
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<div class="section"><p>The CONNECT statement is used with a TO or RESET clause. A CONNECT
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statement with a TO clause allows you to specify connection to a particular
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AS relational database. The CONNECT statement with a RESET clause specifies
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connection to the local relational database.</p>
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</div>
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<div class="section"><p>When you issue (or the program issues) a CONNECT statement with
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a TO or RESET clause, the AS identified must be described in the relational
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database directory. The AR must also be in a connectable state for the CONNECT
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statement to be successful.</p>
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</div>
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<div class="section"><p>The CONNECT statement has different effects depending on the connection
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management method you use. For RUW connection management, the CONNECT statement
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has the following effects: </p>
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<ul><li>When a CONNECT statement with a TO or RESET clause is successful, the
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following events take place: <ul><li>Any open cursors are closed, any prepared statements are discarded, and
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any held resources are released from the previous AS if the application process
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was placed in the connectable state through the use of COMMIT HOLD or ROLLBACK
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HOLD SQL statement, or if the application process is running COMMIT(*NONE).</li>
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<li>The application process is disconnected from its previous AS, if any,
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and connected to the identified AS.</li>
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<li>The name of the AS is placed in the Current Server special register.</li>
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<li>Information that identifies the system module that returned the error
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is placed in the SQLERRP field of the SQL communication area (SQLCA) or in
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DB2_MODULE_DETECTING_ERROR of the SQL diagnostic area.</li>
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</ul>
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</li>
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<li>If the CONNECT statement is unsuccessful for any reason, the application
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remains in the connectable but unconnected state. An application in the connectable
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but unconnected state can only run the CONNECT statement.</li>
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<li>Consecutive CONNECT statements can be run successfully because CONNECT
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does not remove the AR from the connectable state. A CONNECT to the AS to
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which the AR is currently connected is run like any other CONNECT statement.</li>
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<li>If running with commitment control, the CONNECT statement cannot run successfully
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when it is preceded by any SQL statement other than CONNECT, SET CONNECTION,
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COMMIT, ROLLBACK, DISCONNECT, or RELEASE. To avoid an error, perform a COMMIT
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or ROLLBACK operation before a CONNECT statement is run. If running without
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commitment control, the CONNECT statement is always allowed.</li>
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</ul>
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</div>
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<div class="section"><p>For DUW connection management, the CONNECT statement has the following
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effects: </p>
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<ul><li>When a CONNECT statement with a TO or RESET clause is successful, the
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following events take place: <ul><li>The name of the AS is placed in the Current Server special register.</li>
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<li>Information that identifies the system module that returned the error
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is placed in the SQLERRP field of the SQL communication area (SQLCA) or in
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DB2_MODULE_DETECTING_ERROR of the SQL diagnostic area.</li>
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<li id="rbal1excon__rbal1sql45"><a name="rbal1excon__rbal1sql45"><!-- --></a>Information on the type of connection is also placed into
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the SQLCA and SQL diagnostic area. Encoded in these is the following information: <ul><li>Whether the application is in a connected or unconnected state can be
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found in SQLERRD(5) in the SQLCA or in DB2_CONNECTION_STATE in the SQL diagnostic
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area.</li>
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<li>Whether a remote connection uses a protected or unprotected conversation
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is found in SQLERRD(4) in the SQLCA or in DB2_CONNECTION_TYPE in the SQL diagnostic
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area. </li>
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<li>Whether the connection is always read-only, always capable of updates,
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or whether the ability to update can change between each unit of work is found
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in SQLERRD(4) in the SQLCA or in DB2_CONNECTION_STATUS in the SQL diagnostic
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area.</li>
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</ul>
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<p>See the <a href="../sqlp/rbafykickoff.htm">SQL
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programming</a> topic for more information about SQLERRD fields in the
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SQLCA and about connection information in the SQL diagnostic area.</p>
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</li>
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</ul>
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</li>
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<li>If the CONNECT statement with a TO or RESET clause is unsuccessful because
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the AR is not in the connectable state or the <span class="synph"><span class="var">server-name</span></span> is
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not listed in the local relational database directory, the connection state
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of the AR is unchanged.</li>
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<li>A connection to a currently connected AS results in an error.</li>
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<li>A connection without a TO or RESET clause can be used to obtain information
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about the current connection. This includes the following information: <ul><li>Information that identifies the system module that returned the status
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is placed in the SQLERRP field of the SQL communication area (SQLCA) or in
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DB2_MODULE_DETECTING_ERROR of the SQL diagnostic area.</li>
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<li>Other status information is described in the previous paragraphs
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discussing the contents of SQLERRD(4) and SQLERRD(5) and the corresponding
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information in the SQL diagnostic area.</li>
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</ul>
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</li>
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</ul>
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</div>
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<div class="section"><p>It is a good practice for the first SQL statement run by an application
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process to be the CONNECT statement. However, when you have CONNECT statements
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embedded in your program you might want to dynamically change the AS name
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if the program connects to more than one AS. If you are going to run the application
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at multiple servers, you can specify the CONNECT statement with a host variable
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as shown here, so that the program can be passed the relational database name.</p>
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<pre>CONNECT TO : host-variable</pre>
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</div>
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<div class="section"><p>Without CONNECT statements, all you need to do when you change
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the AS is to recompile the program with the new relational database name.</p>
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</div>
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<div class="section"><p>The following example shows two forms of the CONNECT statement
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(<strong><span>1</span></strong> and <strong><span>2</span></strong>) in an application program: </p>
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<pre>CRTSQL<em>xxx</em> PGM(SPIFFY/FIXTOTAL) COMMIT(*CHG) RDB(KC105)
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PROC: FIXTOTAL;
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EXEC SQL CONNECT TO KC105; <strong><span>1</span></strong>
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EXEC SQL
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SELECT * INTO :SERVICE
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FROM REPAIRTOT;
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EXEC SQL COMMIT;
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EXEC SQL CONNECT TO MPLS03 USER :USERID USING :PW; <strong><span>2</span></strong>
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EXEC SQL SELECT …
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EXEC SQL COMMIT;
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END FIXTOTAL;</pre>
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</div>
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<div class="section"><p>The example (<strong><span>2</span></strong>) shows the use of the USER/USING
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form of the CONNECT statement. You must specify the user ID and password with
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host variables when this form of the CONNECT statement is embedded in a program.
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If you are using TCP/IP, a user ID and password can be extracted
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from a security object at connect time if you have used the <span class="cmdname">Add Server
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Authentication Entry (ADDSVRAUTE)</span> command with the appropriate parameters
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to store them.</p>
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</div>
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<div class="section"><p>The following example shows both CONNECT statement forms in Interactive
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SQL. Note that the password must be enclosed in single quotation marks.</p>
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<pre class="screen">Type SQL statement, press Enter.
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Current connection is to relational database (RDB) KC105.
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CONNECT TO KC000_________________________________________________________
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COMMIT___________________________________________________________________
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===> CONNECT TO MPLS03 USER JOE USING 'X47K'_____________________________
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_________________________________________________________________________
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_________________________________________________________________________
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</pre>
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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="rbal1cnct.htm" title="What makes a distributed relational database application distributed is its ability to connect to a relational database on another server.">Connect to a distributed relational database</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="rbal1rdbdir.htm" title="The i5/OS licensed program uses the relational database directory to define the relational database names that can be accessed by applications running on an iSeries server, to specify if the connection uses Systems Network Architecture (SNA) or IP, and to associate these relational database names with their corresponding network parameters.">Use the relational database directory</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="rbal1ddmcnv.htm" title="The term connection in this topic collection refers to the concept of an SQL connection. An SQL connection lasts from the time an explicit or implicit SQL CONNECT is done until the logical SQL connection is terminated by such means as an SQL DISCONNECT, or a RELEASE followed by a COMMIT.">Control DDM conversations</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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