164 lines
8.2 KiB
HTML
164 lines
8.2 KiB
HTML
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<meta name="DC.Title" content="Retrieve results" />
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<meta name="abstract" content="In order to work with all of the rows in a result set, call the SQLFetch API until no more rows are returned." />
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<link rel="stylesheet" type="text/css" href="./ic.css" />
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<title>Retrieve results</title>
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</head>
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<body id="retrieveresults"><a name="retrieveresults"><!-- --></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">Retrieve results</h1>
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<div><p>In order to work with all of the rows in a result set, call the <strong>SQLFetch</strong> API
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until no more rows are returned.</p>
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<div class="section"><p>Running some <span class="keyword">SQL</span> statements
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returns results to the application program. Running an <span class="keyword">SQL</span> SELECT
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statement returns the selected rows in a result set. The <strong><span class="keyword">SQL</span>Fetch</strong> API
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then sequentially retrieves the selected rows from the result set into the
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application program's internal storage. </p>
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</div>
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<div class="section"><p>You also may issue a Select statement where you do not specify
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what columns you want returned. For example, <samp class="codeph">SELECT * FROM RWM.DBFIL</samp> selects
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all columns. You may not know what columns or how many columns will be returned. </p>
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<dl><dt class="dlterm">SQLNumResultCols</dt>
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<dd>Returns the number of columns in a result set. <ul><li>A storage buffer that receives the information is passed as a parameter.</li>
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</ul>
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<pre> SQLSMALLINT nResultCols;
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rc = SQLNumResultCols(hstmt, &nResultCols);</pre>
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</dd>
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<dt class="dlterm">SQLDescribeCol</dt>
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<dd>Returns the result descriptor for one column in a result set. <ul><li><strong>Column name</strong></li>
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<li><strong>Column type</strong></li>
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<li><strong>Column size</strong> <p>This is used with <strong>SQLNumResultCols</strong> to retrieve
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information about the columns returned. Using this approach, as opposed to
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hard coding the information in the program, makes for more flexible programs.</p>
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<p>The
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programmer first uses <strong>SQLNumResultCols</strong> to find out how many columns
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were returned in the result set by a select statement. Then a loop is set
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up to use <strong>SQLDescribeCol</strong> to retrieve information about each column.</p>
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</li>
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</ul>
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<p>In C, this statement is coded: </p>
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<pre>
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SQLCHAR szColName[51];
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SQLSMALLINT lenColName, colSQLtype, scale, nullable;
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SQLUSMALLINT colNum = 1;
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SQLUINTEGER cbColDef;
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rc = SQLDescribeCol(hstmt, colNum, szColName, sizeof(szColName),
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&lenColName, &colSQLtype, &cbColDef, &scale, &nullable);</pre>
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</dd>
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<dt class="dlterm">SQLBindCol</dt>
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<dd>Assigns the storage and data type for a column in a result set: <ul><li>Storage buffer that receives the information.</li>
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<li>Length of storage buffer.</li>
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<li>Data type conversion.</li>
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</ul>
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<p>In C, this statement is coded: </p>
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<pre>SQLUSMALLINT colNum = 1;
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SQLUINTEGER cbColDef;
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SQLINTEGER idNum, indPtr, strlen_or_indPtr;
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SQLCHAR szIDName[51];
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colNum = 1;
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rc = SQLBindCol(hstmt, colNum, SQL_C_LONG, &idNum, sizeof(SQLINTEGER), &indPtr);
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colNum = 2;
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rc = SQLBindCol(hstmt, colNum, SQL_C_CHAR, szIDName, sizeof(szIDName), &strlen_or_indPtr);</pre>
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<div class="note"><span class="notetitle">Note:</span> If
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you use this with Visual Basic, it is recommended that you use an array of
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Byte data type in place of String data types.</div>
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</dd>
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<dt class="dlterm">SQLFetch</dt>
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<dd>Each time <strong>SQLFetch</strong> is called, the driver fetches the next row.
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Bound columns are stored in the locations specified. Data for unbound columns
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may be retrieved using <strong>SQLGetData</strong>. <div class="p">In C, this statement is coded:
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<pre>rc = SQLFetch(hstmt);</pre>
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</div>
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<p>Visual Basic does not directly support
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pointers or fixed memory location ANSI character null-terminated strings.
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For this reason, it is best to use another method to bind Character and Binary
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parameters. One method is to convert Visual Basic String data types to/from
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an array of Byte data types and bind the array of Byte. Another method is
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to use the <strong>SQLGetData</strong> function instead of <strong>SQLBindCol</strong>.</p>
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</dd>
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<dt class="dlterm">SQLGetData</dt>
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<dd>Retrieves data for unbound columns after a fetch. In this example, three
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columns are returned and <strong>SQLGetData</strong> is used to move them to the correct
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storage location. <p>In C, this statement is coded: </p>
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<pre>SQLCHAR szTheName[16], szCredit[2];
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float iDiscount, iTax;
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rc = SQLFetch(hstmt);
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rc = SQLGetData(hstmt, 1, SQL_C_CHAR, szTheName, 16, &strlen_or_indPtr);
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rc = SQLGetData(hstmt, 2, SQL_C_FLOAT, &iDiscount, sizeof(float), &indPtr);
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rc = SQLGetData(hstmt, 3, SQL_C_CHAR, szCredit, 2, &strlen_or_indPtr);
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rc = SQLGetData(hstmt, 4, SQL_C_FLOAT, &iTax, sizeof(float), &indPtr);
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</pre>
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<p>In Visual Basic, this statement is coded: </p>
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<pre> rc = SQLFetch(hStmt)
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If rc = SQL_NO_DATA_FOUND Then
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Call DisplayWarning("No record found!")
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rc = SQLCloseCursor(hStmt)
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If rc <> SQL_SUCCESS Then
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Call DspSQLDiagRec(SQL_HANDLE_STMT, hStmt, "Close cursor failed.")
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End If
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Else
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' Reset lcbBuffer for the call to SQLGetData
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lcbBuffer = 0
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'Get part ID from the fetched record
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rc = SQLGetData(hStmt, 1, SQL_C_LONG, _
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lPartIDReceived, Len(lPartIDReceived), lcbBuffer)
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If rc <> SQL_SUCCESS And rc <> SQL_SUCCESS_WITH_INFO Then _
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Call DspSQLDiagRec(SQL_HANDLE_STMT, hStmt, _
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"Problem getting data for PartID column")
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'Get part description from the fetched record
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rc = SQLGetData(hStmt, 2, SQL_C_CHAR, _
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szDescription(0), 257, lcbBuffer)
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If rc <> SQL_SUCCESS And rc <> SQL_SUCCESS_WITH_INFO Then _
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Call DspSQLDiagRec(SQL_HANDLE_STMT, hStmt, _
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"Problem getting data for PartDescription column")
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'Get part provider from the fetched record
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rc = SQLGetData(hStmt, 3, SQL_C_CHAR, _
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szProvider(0), 257, lcbBuffer)
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If rc <> SQL_SUCCESS And rc <> SQL_SUCCESS_WITH_INFO Then _
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Call DspSQLDiagRec(SQL_HANDLE_STMT, hStmt, _
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"Problem getting data for PartProvider column")
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Call DisplayMessage("Record found!")
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rc = SQLCloseCursor(hStmt)
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If rc <> SQL_SUCCESS Then _
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Call DspSQLDiagRec(SQL_HANDLE_STMT, hStmt, "Close cursor failed.")
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End If</pre>
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</dd>
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</dl>
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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="rzaikodbcapiinfo.htm" title="Identify the files required to build an ODBC application.">Files required to build an ODBC application</a></div>
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</div>
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</div>
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</body>
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</html> |