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CLI query results processing routines
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/* Establish a cursor name for an open cursor */ short SQLSetCursorName ( long stmtHdl, char short cursname, namelen) /* IN: /* IN: /* IN: statement handle */ name for cursor */ length of cursor name */
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/* Retrieve the name of an open cursor */ short SQLGetCursorName ( long char short stmtHdl, cursname, buflen, /* IN: /* IN: statement handle */ length of buffer */ /* OUT: buffer for returned name */ /* OUT: actual length of returned name */
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short *namlen)
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CLI query results processing routines (continued)
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The program excerpt in Figure 19-18 shows a simple query carried out using this technique. The program is identical in function to the dblib-based program example in Figure 19-7. It s instructive to compare the two programs. The specifics of the calls
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/* Program to display a report of sales reps over quota */ #include <sqlcli.h> /* header file with CLI definitions */ main() { SQLHENV env_hdl; /* SQL-environment handle */ SQLHDBC conn_hdl; /* connection handle */ SQLHSTMT stmt_hdl; /* statement handle */ SQLRETURN status; /* CLI routine return status */ char *svr_name = demo ; /* server name */ char *user_name = joe ; /* user name for connection */ char *user_pswd = xyz ; /* user password for connection */ char repname[16]; /* retrieved salesperson s name */ float repquota; /* retrieved quota */ float repsales; /* retrieved sales */ short repquota_ind; /* NULL quota indicator */ char stmt_buf[128]; /* buffer for SQL statement */
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PROGRAMMING WITH SQL
Figure 19-18.
Retrieving CLI query results
SQL: The Complete Reference
/* Allocate handles and connect to the database */ SQLAllocHandle(SQL_HANDLE_ENV, SQL_NULL_HANDLE, &env_hdl); SQLAllocHandle(SQL_HANDLE_DBC, env_hdl, &conn_hdl); SQLAllocHandle(SQL_HANDLE_STMT, conn_hdl, &stmt_hdl); SQLConnect(conn_hdl, svr_name, SQL_NTS, user_name, SQL_NTS, user_pswd, SQL_NTS); /* Request execution of the query */ strcpy(stmt_buf, select name, quota, sales from salesreps ); strcat(stmt_buf, where sales > quota order by name ); SQLExecDirect(stmt_hdl, stmt_buf, SQL_NTS); / * Bind retrieved columns to the program s buffers */ SQLBindCol(stmt_hdl,1,SQL_C_CHAR,repname,15,NULL); SQLBindCol(stmt_hdl,2,SQL_C_FLOAT,&repquota,0,"a_ind); SQLBindCol(stmt_hdl,3,SQL_C_FLOAT,&repsales,0,NULL); / * Loop through each row of query results */ for ( ; ; ) { /* Fetch the next row of query results */ if (SQLFetch(stmt_hdl) != SQL_SUCCESS) break; /* Display the retrieved data */ printf( Name: %s\n , repname); if (repquota_ind < 0) printf( Quota is NULL\n ); else printf( Quota: %f\n , repquota); printf( Sales: %f\n , repsales); } / * Disconnect, deallocate handles and exit */ SQLDisconnect(conn_hdl); SQLFreeHandle(SQL_HANDLE_STMT, stmt_hdl); SQLFreeHandle(SQL_HANDLE_DBC, conn_hdl); SQLFreeHandle(SQL_HANDLE_ENV, env_hdl); exit();
Figure 19-18.
Retrieving CLI query results (continued)
19:
SQL APIs
and their parameters are quite different, but the flow of the programs and the logical sequence of calls that they make are the same. Each call to SQLBindCol() establishes an association between one column of query results (identified by column number) and an application program buffer (identified by its address). With each call to SQLFetch(), the CLI uses this binding to copy the appropriate data value for the column into the program s buffer area. When appropriate, a second program data area is specified as the indicator-variable buffer for the column. Each call to SQLFetch() sets this program variable to indicate the actual length of the returned data value (for variable-length data) and to indicate when a NULL value is returned. When the program has finished processing all of the query results, it calls SQLCloseCursor(). The CLI routines in Figure 19-17 can also be used to implement an alternative method of processing query results. In this technique, the columns of query results are not bound to locations in the application program in advance. Instead, each call to SQLFetch() only advances the cursor to the next row of query results. It does not actually cause retrieval of data into host program data areas. Instead, a call to SQLGetData() is made to actually retrieve the data. One of the parameters of SQLGetData() specifies which column of query results is to be retrieved. The other parameters specify the data type to be returned and the location of the buffer to receive the data and an associated indicator variable value. At the basic level, the SQLGetData()call is simply an alternative to the host-variable binding approach provided by SQLBindCol(), but SQLGetData() provides an important advantage when processing very large data items. Some databases support long binary or character-valued columns that can contain thousands or millions of bytes of data. It s usually impractical to allocate a program buffer to hold all of the data in such a column. Using SQLGetData(), the program can allocate a buffer of reasonable size and work its way through the data a few thousand bytes at a time. It s possible to intermix the SQLBindCol() and SQLGetData() styles to process the query results of a single statement. In this case, the SQLFetch() call actually retrieves the data values for the bound columns (those for which a SQLBindCol() call has been made), but the program must explicitly call SQLGetData() to process the other columns. This technique may be especially appropriate if a query retrieves several columns of typical SQL data (names, dates, money amounts) and a column or two of long data, such as the text of a contract. Note that some CLI implementations severely restrict the ability to intermix the two styles of processing. In particular, some implementations require that all of the bound columns appear first in the left-to-right order of query results, before any columns retrieved using SQLGetData().
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